src/library_pthread.js

/**
 * @license
 * Copyright 2015 The Emscripten Authors
 * SPDX-License-Identifier: MIT
 *
 * Because only modern JS engines support SAB we can use modern JS language
 * features within this file (ES2020).
 */

#if !PTHREADS
#error "Internal error! PTHREADS should be enabled when including library_pthread.js."
#endif
#if !SHARED_MEMORY
#error "Internal error! SHARED_MEMORY should be enabled when including library_pthread.js."
#endif
#if PTHREADS == 2
#error "PTHREADS=2 is no longer supported"
#endif
#if BUILD_AS_WORKER
#error "pthreads + BUILD_AS_WORKER require separate modes that don't work together, see https://github.com/emscripten-core/emscripten/issues/8854"
#endif
#if EVAL_CTORS
#error "EVAL_CTORS is not compatible with pthreads yet (passive segments)"
#endif

var LibraryPThread = {
  $PThread__postset: 'PThread.init();',
  $PThread__deps: ['_emscripten_thread_init',
                   '$killThread',
                   '$cancelThread', '$cleanupThread', '$zeroMemory',
#if MAIN_MODULE
                   '$markAsFinshed',
#endif
                   '$spawnThread',
                   '_emscripten_thread_free_data',
                   'exit',
#if PTHREADS_DEBUG || ASSERTIONS
                   '$ptrToString',
#endif
#if !MINIMAL_RUNTIME
                   '$handleException',
#endif
                   ],
  $PThread: {
    // Contains all Workers that are idle/unused and not currently hosting an
    // executing pthread.  Unused Workers can either be pooled up before page
    // startup, but also when a pthread quits, its hosting Worker is not
    // terminated, but is returned to this pool as an optimization so that
    // starting the next thread is faster.
    unusedWorkers: [],
    // Contains all Workers that are currently hosting an active pthread.
    runningWorkers: [],
    tlsInitFunctions: [],
    // Maps pthread_t pointers to the workers on which they are running.  For
    // the reverse mapping, each worker has a `pthread_ptr` when its running a
    // pthread.
    pthreads: {},
#if ASSERTIONS
    nextWorkerID: 1,
    debugInit: function() {
      function pthreadLogPrefix() {
        var t = 0;
        if (runtimeInitialized && typeof _pthread_self != 'undefined'
#if EXIT_RUNTIME
        && !runtimeExited
#endif
        ) {
          t = _pthread_self();
        }
        return 'w:' + (Module['workerID'] || 0) + ',t:' + ptrToString(t) + ': ';
      }

      // Prefix all err()/dbg() messages with the calling thread ID.
      var origDbg = dbg;
      dbg = (message) => origDbg(pthreadLogPrefix() + message);
#if PTHREADS_DEBUG
      // With PTHREADS_DEBUG also prefix all err() messages.
      var origErr = err;
      err = (message) => origErr(pthreadLogPrefix() + message);
#endif
    },
#endif
    init: function() {
#if ASSERTIONS
      PThread.debugInit();
#endif
      if (ENVIRONMENT_IS_PTHREAD
#if AUDIO_WORKLET
        || ENVIRONMENT_IS_AUDIO_WORKLET
#endif
        ) {
        PThread.initWorker();
      } else {
        PThread.initMainThread();
      }
    },
    initMainThread: function() {
#if PTHREAD_POOL_SIZE
      var pthreadPoolSize = {{{ PTHREAD_POOL_SIZE }}};
      // Start loading up the Worker pool, if requested.
      while (pthreadPoolSize--) {
        PThread.allocateUnusedWorker();
      }
#endif
#if !MINIMAL_RUNTIME
      // MINIMAL_RUNTIME takes care of calling loadWasmModuleToAllWorkers
      // in postamble_minimal.js
      addOnPreRun(() => {
        addRunDependency('loading-workers')
        PThread.loadWasmModuleToAllWorkers(() => removeRunDependency('loading-workers'));
      });
#endif
#if MAIN_MODULE
      PThread.outstandingPromises = {};
      // Finished threads are threads that have finished running but we not yet
      // joined.
      PThread.finishedThreads = new Set();
#endif
    },

    initWorker: function() {
#if USE_CLOSURE_COMPILER
      // worker.js is not compiled together with us, and must access certain
      // things.
      PThread['receiveObjectTransfer'] = PThread.receiveObjectTransfer;
      PThread['threadInitTLS'] = PThread.threadInitTLS;
#if !MINIMAL_RUNTIME
      PThread['setExitStatus'] = PThread.setExitStatus;
#endif
#endif

#if !MINIMAL_RUNTIME
      // The default behaviour for pthreads is always to exit once they return
      // from their entry point (or call pthread_exit).  If we set noExitRuntime
      // to true here on pthreads they would never complete and attempt to
      // pthread_join to them would block forever.
      // pthreads can still choose to set `noExitRuntime` explicitly, or
      // call emscripten_unwind_to_js_event_loop to extend their lifetime beyond
      // their main function.  See comment in src/worker.js for more.
      noExitRuntime = false;
#endif
    },

#if PTHREADS_PROFILING
    getThreadName: function(pthreadPtr) {
      var profilerBlock = {{{ makeGetValue('pthreadPtr', C_STRUCTS.pthread.profilerBlock, POINTER_TYPE) }}};
      if (!profilerBlock) return "";
      return UTF8ToString(profilerBlock + {{{ C_STRUCTS.thread_profiler_block.name }}});
    },

    threadStatusToString: function(threadStatus) {
      switch (threadStatus) {
        case 0: return "not yet started";
        case 1: return "running";
        case 2: return "sleeping";
        case 3: return "waiting for a futex";
        case 4: return "waiting for a mutex";
        case 5: return "waiting for a proxied operation";
        case 6: return "finished execution";
        default: return "unknown (corrupt?!)";
      }
    },

    threadStatusAsString: function(pthreadPtr) {
      var profilerBlock = {{{ makeGetValue('pthreadPtr', C_STRUCTS.pthread.profilerBlock, POINTER_TYPE) }}};
      var status = (profilerBlock == 0) ? 0 : Atomics.load(HEAPU32, (profilerBlock + {{{ C_STRUCTS.thread_profiler_block.threadStatus }}} ) >> 2);
      return PThread.threadStatusToString(status);
    },
#endif

#if !MINIMAL_RUNTIME
    setExitStatus: function(status) {
      EXITSTATUS = status;
    },
#endif

    terminateAllThreads__deps: ['$terminateWorker'],
    terminateAllThreads: function() {
#if ASSERTIONS
      assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! terminateAllThreads() can only ever be called from main application thread!');
#endif
#if PTHREADS_DEBUG
      dbg('terminateAllThreads');
#endif
      // Attempt to kill all workers.  Sadly (at least on the web) there is no
      // way to terminate a worker synchronously, or to be notified when a
      // worker in actually terminated.  This means there is some risk that
      // pthreads will continue to be executing after `worker.terminate` has
      // returned.  For this reason, we don't call `returnWorkerToPool` here or
      // free the underlying pthread data structures.
      for (var worker of PThread.runningWorkers) {
        terminateWorker(worker);
      }
      for (var worker of PThread.unusedWorkers) {
        terminateWorker(worker);
      }
      PThread.unusedWorkers = [];
      PThread.runningWorkers = [];
      PThread.pthreads = [];
    },
    returnWorkerToPool: function(worker) {
      // We don't want to run main thread queued calls here, since we are doing
      // some operations that leave the worker queue in an invalid state until
      // we are completely done (it would be bad if free() ends up calling a
      // queued pthread_create which looks at the global data structures we are
      // modifying). To achieve that, defer the free() til the very end, when
      // we are all done.
      var pthread_ptr = worker.pthread_ptr;
      delete PThread.pthreads[pthread_ptr];
      // Note: worker is intentionally not terminated so the pool can
      // dynamically grow.
      PThread.unusedWorkers.push(worker);
      PThread.runningWorkers.splice(PThread.runningWorkers.indexOf(worker), 1);
      // Not a running Worker anymore
      // Detach the worker from the pthread object, and return it to the
      // worker pool as an unused worker.
      worker.pthread_ptr = 0;

#if ENVIRONMENT_MAY_BE_NODE && PROXY_TO_PTHREAD
      if (ENVIRONMENT_IS_NODE) {
        // Once the proxied main thread has finished, mark it as weakly
        // referenced so that its existence does not prevent Node.js from
        // exiting.  This has no effect if the worker is already weakly
        // referenced.
        worker.unref();
      }
#endif

      // Finally, free the underlying (and now-unused) pthread structure in
      // linear memory.
      __emscripten_thread_free_data(pthread_ptr);
    },
    receiveObjectTransfer: function(data) {
#if OFFSCREENCANVAS_SUPPORT
      if (typeof GL != 'undefined') {
        Object.assign(GL.offscreenCanvases, data.offscreenCanvases);
        if (!Module['canvas'] && data.moduleCanvasId && GL.offscreenCanvases[data.moduleCanvasId]) {
          Module['canvas'] = GL.offscreenCanvases[data.moduleCanvasId].offscreenCanvas;
          Module['canvas'].id = data.moduleCanvasId;
        }
      }
#endif
    },
    // Called by worker.js each time a thread is started.
    threadInitTLS: function() {
#if PTHREADS_DEBUG
      dbg('threadInitTLS');
#endif
      // Call thread init functions (these are the _emscripten_tls_init for each
      // module loaded.
      PThread.tlsInitFunctions.forEach((f) => f());
    },
    // Loads the WebAssembly module into the given Worker.
    // onFinishedLoading: A callback function that will be called once all of
    //                    the workers have been initialized and are
    //                    ready to host pthreads.
    loadWasmModuleToWorker: (worker) => new Promise((onFinishedLoading) => {
      worker.onmessage = (e) => {
        var d = e['data'];
        var cmd = d['cmd'];

        // If this message is intended to a recipient that is not the main thread, forward it to the target thread.
        if (d['targetThread'] && d['targetThread'] != _pthread_self()) {
          var targetWorker = PThread.pthreads[d.targetThread];
          if (targetWorker) {
            targetWorker.postMessage(d, d['transferList']);
          } else {
            err('Internal error! Worker sent a message "' + cmd + '" to target pthread ' + d['targetThread'] + ', but that thread no longer exists!');
          }
          return;
        }

        if (cmd === 'checkMailbox') {
          checkMailbox();
        } else if (cmd === 'spawnThread') {
          spawnThread(d);
        } else if (cmd === 'cleanupThread') {
          cleanupThread(d['thread']);
#if MAIN_MODULE
        } else if (cmd === 'markAsFinshed') {
          markAsFinshed(d['thread']);
#endif
        } else if (cmd === 'killThread') {
          killThread(d['thread']);
        } else if (cmd === 'cancelThread') {
          cancelThread(d['thread']);
        } else if (cmd === 'loaded') {
          worker.loaded = true;
#if ENVIRONMENT_MAY_BE_NODE && PTHREAD_POOL_SIZE
          // Check that this worker doesn't have an associated pthread.
          if (ENVIRONMENT_IS_NODE && !worker.pthread_ptr) {
            // Once worker is loaded & idle, mark it as weakly referenced,
            // so that mere existence of a Worker in the pool does not prevent
            // Node.js from exiting the app.
            worker.unref();
          }
#endif
          onFinishedLoading(worker);
        } else if (cmd === 'alert') {
          alert('Thread ' + d['threadId'] + ': ' + d['text']);
        } else if (d.target === 'setimmediate') {
          // Worker wants to postMessage() to itself to implement setImmediate()
          // emulation.
          worker.postMessage(d);
        } else if (cmd === 'callHandler') {
          Module[d['handler']](...d['args']);
        } else if (cmd) {
          // The received message looks like something that should be handled by this message
          // handler, (since there is a e.data.cmd field present), but is not one of the
          // recognized commands:
          err("worker sent an unknown command " + cmd);
        }
      };

      worker.onerror = (e) => {
        var message = 'worker sent an error!';
#if ASSERTIONS
        if (worker.pthread_ptr) {
          message = 'Pthread ' + ptrToString(worker.pthread_ptr) + ' sent an error!';
        }
#endif
        err(message + ' ' + e.filename + ':' + e.lineno + ': ' + e.message);
        throw e;
      };

#if ENVIRONMENT_MAY_BE_NODE
      if (ENVIRONMENT_IS_NODE) {
        worker.on('message', function(data) {
          worker.onmessage({ data: data });
        });
        worker.on('error', function(e) {
          worker.onerror(e);
        });
      }
#endif

#if ASSERTIONS
      assert(wasmMemory instanceof WebAssembly.Memory, 'WebAssembly memory should have been loaded by now!');
      assert(wasmModule instanceof WebAssembly.Module, 'WebAssembly Module should have been loaded by now!');
#endif

      // When running on a pthread, none of the incoming parameters on the module
      // object are present. Proxy known handlers back to the main thread if specified.
      var handlers = [];
      var knownHandlers = [
#if expectToReceiveOnModule('onExit')
        'onExit',
#endif
#if expectToReceiveOnModule('onAbort')
        'onAbort',
#endif
#if expectToReceiveOnModule('print')
        'print',
#endif
#if expectToReceiveOnModule('printErr')
        'printErr',
#endif
      ];
      for (var handler of knownHandlers) {
        if (Module.hasOwnProperty(handler)) {
          handlers.push(handler);
        }
      }

#if ASSERTIONS
      worker.workerID = PThread.nextWorkerID++;
#endif

      // Ask the new worker to load up the Emscripten-compiled page. This is a heavy operation.
      worker.postMessage({
        'cmd': 'load',
        'handlers': handlers,
        // If the application main .js file was loaded from a Blob, then it is not possible
        // to access the URL of the current script that could be passed to a Web Worker so that
        // it could load up the same file. In that case, developer must either deliver the Blob
        // object in Module['mainScriptUrlOrBlob'], or a URL to it, so that pthread Workers can
        // independently load up the same main application file.
        'urlOrBlob': Module['mainScriptUrlOrBlob']
#if !EXPORT_ES6
        || _scriptDir
#endif
        ,
#if WASM2JS
        // the polyfill WebAssembly.Memory instance has function properties,
        // which will fail in postMessage, so just send a custom object with the
        // property we need, the buffer
        'wasmMemory': { 'buffer': wasmMemory.buffer },
#else // WASM2JS
        'wasmMemory': wasmMemory,
#endif // WASM2JS
        'wasmModule': wasmModule,
#if LOAD_SOURCE_MAP
        'wasmSourceMap': wasmSourceMap,
#endif
#if USE_OFFSET_CONVERTER
        'wasmOffsetConverter': wasmOffsetConverter,
#endif
#if MAIN_MODULE
        // Share all modules that have been loaded so far.  New workers
        // won't start running threads until these are all loaded.
        'sharedModules': sharedModules,
#endif
#if ASSERTIONS
        'workerID': worker.workerID,
#endif
      });
    }),

    loadWasmModuleToAllWorkers: function(onMaybeReady) {
#if !PTHREAD_POOL_SIZE
      onMaybeReady();
#else
      // Instantiation is synchronous in pthreads.
      if (
        ENVIRONMENT_IS_PTHREAD
#if WASM_WORKERS
        || ENVIRONMENT_IS_WASM_WORKER
#endif
      ) {
        return onMaybeReady();
      }

      let pthreadPoolReady = Promise.all(PThread.unusedWorkers.map(PThread.loadWasmModuleToWorker));
#if PTHREAD_POOL_DELAY_LOAD
      // PTHREAD_POOL_DELAY_LOAD means we want to proceed synchronously without
      // waiting for the pthread pool during the startup phase.
      // If the user wants to wait on it elsewhere, they can do so via the
      // Module['pthreadPoolReady'] promise.
      Module['pthreadPoolReady'] = pthreadPoolReady;
      onMaybeReady();
#else
      pthreadPoolReady.then(onMaybeReady);
#endif // PTHREAD_POOL_DELAY_LOAD
#endif // PTHREAD_POOL_SIZE
    },

    // Creates a new web Worker and places it in the unused worker pool to wait for its use.
    allocateUnusedWorker: function() {
      var worker;
#if MINIMAL_RUNTIME
      var pthreadMainJs = Module['worker'];
#else
#if EXPORT_ES6 && USE_ES6_IMPORT_META
      // If we're using module output and there's no explicit override, use bundler-friendly pattern.
      if (!Module['locateFile']) {
#if PTHREADS_DEBUG
        dbg('Allocating a new web worker from ' + new URL('{{{ PTHREAD_WORKER_FILE }}}', import.meta.url));
#endif
#if TRUSTED_TYPES
        // Use Trusted Types compatible wrappers.
        if (typeof trustedTypes != 'undefined' && trustedTypes.createPolicy) {
          var p = trustedTypes.createPolicy(
            'emscripten#workerPolicy1',
            {
              createScriptURL: function(ignored) {
                return new URL('{{{ PTHREAD_WORKER_FILE }}}', import.meta.url);
              }
            }
          );
          worker = new Worker(p.createScriptURL('ignored'));
        } else
#endif
        worker = new Worker(new URL('{{{ PTHREAD_WORKER_FILE }}}', import.meta.url));
      } else {
#endif
      // Allow HTML module to configure the location where the 'worker.js' file will be loaded from,
      // via Module.locateFile() function. If not specified, then the default URL 'worker.js' relative
      // to the main html file is loaded.
      var pthreadMainJs = locateFile('{{{ PTHREAD_WORKER_FILE }}}');
#endif
#if PTHREADS_DEBUG
      dbg('Allocating a new web worker from ' + pthreadMainJs);
#endif
#if TRUSTED_TYPES
      // Use Trusted Types compatible wrappers.
      if (typeof trustedTypes != 'undefined' && trustedTypes.createPolicy) {
        var p = trustedTypes.createPolicy('emscripten#workerPolicy2', { createScriptURL: function(ignored) { return pthreadMainJs } });
        worker = new Worker(p.createScriptURL('ignored'));
      } else
#endif
      worker = new Worker(pthreadMainJs);
#if EXPORT_ES6 && USE_ES6_IMPORT_META
    }
#endif
    PThread.unusedWorkers.push(worker);
    },

    getNewWorker: function() {
      if (PThread.unusedWorkers.length == 0) {
// PTHREAD_POOL_SIZE_STRICT should show a warning and, if set to level `2`, return from the function.
#if (PTHREAD_POOL_SIZE_STRICT && ASSERTIONS) || PTHREAD_POOL_SIZE_STRICT == 2
// However, if we're in Node.js, then we can create new workers on the fly and PTHREAD_POOL_SIZE_STRICT
// should be ignored altogether.
#if ENVIRONMENT_MAY_BE_NODE
        if (!ENVIRONMENT_IS_NODE) {
#endif
#if ASSERTIONS
            err('Tried to spawn a new thread, but the thread pool is exhausted.\n' +
            'This might result in a deadlock unless some threads eventually exit or the code explicitly breaks out to the event loop.\n' +
            'If you want to increase the pool size, use setting `-sPTHREAD_POOL_SIZE=...`.'
#if PTHREAD_POOL_SIZE_STRICT == 1
              + '\nIf you want to throw an explicit error instead of the risk of deadlocking in those cases, use setting `-sPTHREAD_POOL_SIZE_STRICT=2`.'
#endif
            );
#endif // ASSERTIONS
#if PTHREAD_POOL_SIZE_STRICT == 2
            return;
#endif
#if ENVIRONMENT_MAY_BE_NODE
        }
#endif
#endif // PTHREAD_POOL_SIZE_STRICT
#if PTHREAD_POOL_SIZE_STRICT < 2 || ENVIRONMENT_MAY_BE_NODE
        PThread.allocateUnusedWorker();
        PThread.loadWasmModuleToWorker(PThread.unusedWorkers[0]);
#endif
      }
      return PThread.unusedWorkers.pop();
    }
  },

  $terminateWorker: function(worker) {
#if PTHREADS_DEBUG
    dbg('terminateWorker: ' + worker.workerID);
#endif
    worker.terminate();
    // terminate() can be asynchronous, so in theory the worker can continue
    // to run for some amount of time after termination.  However from our POV
    // the worker now dead and we don't want to hear from it again, so we stub
    // out its message handler here.  This avoids having to check in each of
    // the onmessage handlers if the message was coming from valid worker.
    worker.onmessage = (e) => {
#if ASSERTIONS
      var cmd = e['data']['cmd'];
      err('received "' + cmd + '" command from terminated worker: ' + worker.workerID);
#endif
    };
  },

  $killThread__deps: ['_emscripten_thread_free_data', '$terminateWorker'],
  $killThread: function(pthread_ptr) {
#if PTHREADS_DEBUG
    dbg('killThread ' + ptrToString(pthread_ptr));
#endif
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! killThread() can only ever be called from main application thread!');
    assert(pthread_ptr, 'Internal Error! Null pthread_ptr in killThread!');
#endif
    var worker = PThread.pthreads[pthread_ptr];
    delete PThread.pthreads[pthread_ptr];
    terminateWorker(worker);
    __emscripten_thread_free_data(pthread_ptr);
    // The worker was completely nuked (not just the pthread execution it was hosting), so remove it from running workers
    // but don't put it back to the pool.
    PThread.runningWorkers.splice(PThread.runningWorkers.indexOf(worker), 1); // Not a running Worker anymore.
    worker.pthread_ptr = 0;
  },

  __emscripten_thread_cleanup: function(thread) {
    // Called when a thread needs to be cleaned up so it can be reused.
    // A thread is considered reusable when it either returns from its
    // entry point, calls pthread_exit, or acts upon a cancellation.
    // Detached threads are responsible for calling this themselves,
    // otherwise pthread_join is responsible for calling this.
#if PTHREADS_DEBUG
    dbg('__emscripten_thread_cleanup: ' + ptrToString(thread))
#endif
    if (!ENVIRONMENT_IS_PTHREAD) cleanupThread(thread);
    else postMessage({ 'cmd': 'cleanupThread', 'thread': thread });
  },

  _emscripten_thread_set_strongref: function(thread) {
    // Called when a thread needs to be strongly referenced.
    // Currently only used for:
    // - keeping the "main" thread alive in PROXY_TO_PTHREAD mode;
    // - crashed threads that needs to propagate the uncaught exception 
    //   back to the main thread.
#if ENVIRONMENT_MAY_BE_NODE
    if (ENVIRONMENT_IS_NODE) {
      PThread.pthreads[thread].ref();
    }
#endif
  },

  $cleanupThread: function(pthread_ptr) {
#if PTHREADS_DEBUG
    dbg('cleanupThread: ' + ptrToString(pthread_ptr))
#endif
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! cleanupThread() can only ever be called from main application thread!');
    assert(pthread_ptr, 'Internal Error! Null pthread_ptr in cleanupThread!');
#endif
    var worker = PThread.pthreads[pthread_ptr];
#if MAIN_MODULE
    PThread.finishedThreads.delete(pthread_ptr);
    if (pthread_ptr in PThread.outstandingPromises) {
      PThread.outstandingPromises[pthread_ptr].resolve();
    }
#endif
    assert(worker);
    PThread.returnWorkerToPool(worker);
  },

#if MAIN_MODULE
  $registerTLSInit: function(tlsInitFunc, moduleExports, metadata) {
#if DYLINK_DEBUG
    dbg("registerTLSInit: " + tlsInitFunc);
#endif
    // In relocatable builds, we use the result of calling tlsInitFunc
    // (`_emscripten_tls_init`) to relocate the TLS exports of the module
    // according to this new __tls_base.
    function tlsInitWrapper() {
      var __tls_base = tlsInitFunc();
#if DYLINK_DEBUG
      dbg('tlsInit -> ' + __tls_base);
#endif
      if (!__tls_base) {
#if ASSERTIONS
        // __tls_base should never be zero if there are tls exports
        assert(__tls_base || metadata.tlsExports.size == 0);
#endif
        return;
      }
      var tlsExports = {};
      metadata.tlsExports.forEach((s) => tlsExports[s] = moduleExports[s]);
      relocateExports(tlsExports, __tls_base, /*replace=*/true);
    }

    // Register this function so that its gets called for each thread on
    // startup.
    PThread.tlsInitFunctions.push(tlsInitWrapper);

    // If the main thread is already running we also need to call this function
    // now.  If the main thread is not yet running this will happen when it
    // is initialized and processes `PThread.tlsInitFunctions`.
    if (runtimeInitialized) {
      tlsInitWrapper();
    }
  },
#else
  $registerTLSInit: function(tlsInitFunc) {
    PThread.tlsInitFunctions.push(tlsInitFunc);
  },
#endif

  $cancelThread: function(pthread_ptr) {
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! cancelThread() can only ever be called from main application thread!');
    assert(pthread_ptr, 'Internal Error! Null pthread_ptr in cancelThread!');
#endif
    var worker = PThread.pthreads[pthread_ptr];
    worker.postMessage({ 'cmd': 'cancel' });
  },

  $spawnThread: function(threadParams) {
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! spawnThread() can only ever be called from main application thread!');
    assert(threadParams.pthread_ptr, 'Internal error, no pthread ptr!');
#endif

    var worker = PThread.getNewWorker();
    if (!worker) {
      // No available workers in the PThread pool.
      return {{{ cDefs.EAGAIN }}};
    }
#if ASSERTIONS
    assert(!worker.pthread_ptr, 'Internal error!');
#endif

    PThread.runningWorkers.push(worker);

    // Add to pthreads map
    PThread.pthreads[threadParams.pthread_ptr] = worker;

    worker.pthread_ptr = threadParams.pthread_ptr;
    var msg = {
        'cmd': 'run',
        'start_routine': threadParams.startRoutine,
        'arg': threadParams.arg,
        'pthread_ptr': threadParams.pthread_ptr,
    };
#if OFFSCREENCANVAS_SUPPORT
    // Note that we do not need to quote these names because they are only used
    // in this file, and not from the external worker.js.
    msg.moduleCanvasId = threadParams.moduleCanvasId;
    msg.offscreenCanvases = threadParams.offscreenCanvases;
#endif
#if ENVIRONMENT_MAY_BE_NODE
    if (ENVIRONMENT_IS_NODE) {
      // Mark worker as weakly referenced once we start executing a pthread,
      // so that its existence does not prevent Node.js from exiting.  This
      // has no effect if the worker is already weakly referenced (e.g. if
      // this worker was previously idle/unused).
      worker.unref();
    }
#endif
    // Ask the worker to start executing its pthread entry point function.
    worker.postMessage(msg, threadParams.transferList);
    return 0;
  },

  emscripten_has_threading_support: function() {
    return typeof SharedArrayBuffer != 'undefined';
  },

  emscripten_num_logical_cores: function() {
#if ENVIRONMENT_MAY_BE_NODE
    if (ENVIRONMENT_IS_NODE) return require('os').cpus().length;
#endif
    return navigator['hardwareConcurrency'];
  },

  __emscripten_init_main_thread_js: function(tb) {
    // Pass the thread address to the native code where they stored in wasm
    // globals which act as a form of TLS. Global constructors trying
    // to access this value will read the wrong value, but that is UB anyway.
    __emscripten_thread_init(
      tb,
      /*isMainBrowserThread=*/!ENVIRONMENT_IS_WORKER,
      /*isMainRuntimeThread=*/1,
      /*canBlock=*/!ENVIRONMENT_IS_WEB,
      {{{ DEFAULT_PTHREAD_STACK_SIZE }}},
#if PTHREADS_PROFILING
      /*start_profiling=*/true
#endif
    );
    PThread.threadInitTLS();
  },

  $pthreadCreateProxied__internal: true,
  $pthreadCreateProxied__proxy: 'sync',
  $pthreadCreateProxied__deps: ['__pthread_create_js'],
  $pthreadCreateProxied: function(pthread_ptr, attr, startRoutine, arg) {
    return ___pthread_create_js(pthread_ptr, attr, startRoutine, arg);
  },

#if OFFSCREENCANVAS_SUPPORT
  // ASan wraps the emscripten_builtin_pthread_create call in
  // __lsan::ScopedInterceptorDisabler.  Unfortunately, that only disables it on
  // the thread that made the call.  __pthread_create_js gets proxied to the
  // main thread, where LSan is not disabled. This makes it necessary for us to
  // disable LSan here (using __noleakcheck), so that it does not detect
  // pthread's internal allocations as leaks.  If/when we remove all the
  // allocations from __pthread_create_js we could also remove this.
  __pthread_create_js__noleakcheck: true,
#endif
  __pthread_create_js__deps: ['$spawnThread', 'pthread_self', '$pthreadCreateProxied',
#if OFFSCREENCANVAS_SUPPORT
    'malloc',
#endif
  ],
  __pthread_create_js: function(pthread_ptr, attr, startRoutine, arg) {
    if (typeof SharedArrayBuffer == 'undefined') {
      err('Current environment does not support SharedArrayBuffer, pthreads are not available!');
      return {{{ cDefs.EAGAIN }}};
    }
#if PTHREADS_DEBUG
    dbg("createThread: " + ptrToString(pthread_ptr));
#endif

    // List of JS objects that will transfer ownership to the Worker hosting the thread
    var transferList = [];
    var error = 0;

#if OFFSCREENCANVAS_SUPPORT
    // Deduce which WebGL canvases (HTMLCanvasElements or OffscreenCanvases) should be passed over to the
    // Worker that hosts the spawned pthread.
    // Comma-delimited list of CSS selectors that must identify canvases by IDs: "#canvas1, #canvas2, ..."
    var transferredCanvasNames = attr ? {{{ makeGetValue('attr', C_STRUCTS.pthread_attr_t._a_transferredcanvases, POINTER_TYPE) }}} : 0;
#if OFFSCREENCANVASES_TO_PTHREAD
    // Proxied canvases string pointer -1 is used as a special token to fetch
    // whatever canvases were passed to build in -s
    // OFFSCREENCANVASES_TO_PTHREAD= command line.
    if (transferredCanvasNames == (-1 >>> 0)) transferredCanvasNames = '{{{ OFFSCREENCANVASES_TO_PTHREAD }}}';
    else
#endif
    if (transferredCanvasNames) transferredCanvasNames = UTF8ToString(transferredCanvasNames).trim();
    if (transferredCanvasNames) transferredCanvasNames = transferredCanvasNames.split(',');
#if GL_DEBUG
    dbg('pthread_create: transferredCanvasNames="' + transferredCanvasNames + '"');
#endif

    var offscreenCanvases = {}; // Dictionary of OffscreenCanvas objects we'll transfer to the created thread to own
    var moduleCanvasId = Module['canvas'] ? Module['canvas'].id : '';
    // Note that transferredCanvasNames might be null (so we cannot do a for-of loop).
    for (var i in transferredCanvasNames) {
      var name = transferredCanvasNames[i].trim();
      var offscreenCanvasInfo;
      try {
        if (name == '#canvas') {
          if (!Module['canvas']) {
            err('pthread_create: could not find canvas with ID "' + name + '" to transfer to thread!');
            error = {{{ cDefs.EINVAL }}};
            break;
          }
          name = Module['canvas'].id;
        }
#if ASSERTIONS
        assert(typeof GL == 'object', 'OFFSCREENCANVAS_SUPPORT assumes GL is in use (you can force-include it with \'-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$GL\')');
#endif
        if (GL.offscreenCanvases[name]) {
          offscreenCanvasInfo = GL.offscreenCanvases[name];
          GL.offscreenCanvases[name] = null; // This thread no longer owns this canvas.
          if (Module['canvas'] instanceof OffscreenCanvas && name === Module['canvas'].id) Module['canvas'] = null;
        } else if (!ENVIRONMENT_IS_PTHREAD) {
          var canvas = (Module['canvas'] && Module['canvas'].id === name) ? Module['canvas'] : document.querySelector(name);
          if (!canvas) {
            err('pthread_create: could not find canvas with ID "' + name + '" to transfer to thread!');
            error = {{{ cDefs.EINVAL }}};
            break;
          }
          if (canvas.controlTransferredOffscreen) {
            err('pthread_create: cannot transfer canvas with ID "' + name + '" to thread, since the current thread does not have control over it!');
            error = {{{ cDefs.EPERM }}}; // Operation not permitted, some other thread is accessing the canvas.
            break;
          }
          if (canvas.transferControlToOffscreen) {
#if GL_DEBUG
            dbg('pthread_create: canvas.transferControlToOffscreen(), transferring canvas by name "' + name + '" (DOM id="' + canvas.id + '") from main thread to pthread');
#endif
            // Create a shared information block in heap so that we can control
            // the canvas size from any thread.
            if (!canvas.canvasSharedPtr) {
              canvas.canvasSharedPtr = _malloc(12);
              {{{ makeSetValue('canvas.canvasSharedPtr', 0, 'canvas.width', 'i32') }}};
              {{{ makeSetValue('canvas.canvasSharedPtr', 4, 'canvas.height', 'i32') }}};
              {{{ makeSetValue('canvas.canvasSharedPtr', 8, 0, 'i32') }}}; // pthread ptr to the thread that owns this canvas, filled in below.
            }
            offscreenCanvasInfo = {
              offscreenCanvas: canvas.transferControlToOffscreen(),
              canvasSharedPtr: canvas.canvasSharedPtr,
              id: canvas.id
            }
            // After calling canvas.transferControlToOffscreen(), it is no
            // longer possible to access certain operations on the canvas, such
            // as resizing it or obtaining GL contexts via it.
            // Use this field to remember that we have permanently converted
            // this Canvas to be controlled via an OffscreenCanvas (there is no
            // way to undo this in the spec)
            canvas.controlTransferredOffscreen = true;
          } else {
            err('pthread_create: cannot transfer control of canvas "' + name + '" to pthread, because current browser does not support OffscreenCanvas!');
            // If building with OFFSCREEN_FRAMEBUFFER=1 mode, we don't need to
            // be able to transfer control to offscreen, but WebGL can be
            // proxied from worker to main thread.
#if !OFFSCREEN_FRAMEBUFFER
            err('pthread_create: Build with -sOFFSCREEN_FRAMEBUFFER to enable fallback proxying of GL commands from pthread to main thread.');
            return {{{ cDefs.ENOSYS }}}; // Function not implemented, browser doesn't have support for this.
#endif
          }
        }
        if (offscreenCanvasInfo) {
          transferList.push(offscreenCanvasInfo.offscreenCanvas);
          offscreenCanvases[offscreenCanvasInfo.id] = offscreenCanvasInfo;
        }
      } catch(e) {
        err('pthread_create: failed to transfer control of canvas "' + name + '" to OffscreenCanvas! Error: ' + e);
        return {{{ cDefs.EINVAL }}}; // Hitting this might indicate an implementation bug or some other internal error
      }
    }
#endif // OFFSCREENCANVAS_SUPPORT

    // Synchronously proxy the thread creation to main thread if possible. If we
    // need to transfer ownership of objects, then proxy asynchronously via
    // postMessage.
    if (ENVIRONMENT_IS_PTHREAD && (transferList.length === 0 || error)) {
      return pthreadCreateProxied(pthread_ptr, attr, startRoutine, arg);
    }

    // If on the main thread, and accessing Canvas/OffscreenCanvas failed, abort
    // with the detected error.
    if (error) return error;

#if OFFSCREENCANVAS_SUPPORT
    // Register for each of the transferred canvases that the new thread now
    // owns the OffscreenCanvas.
    for (var canvas of Object.values(offscreenCanvases)) {
      // pthread ptr to the thread that owns this canvas.
      {{{ makeSetValue('canvas.canvasSharedPtr', 8, 'pthread_ptr', 'i32') }}};
    }
#endif

    var threadParams = {
      startRoutine,
      pthread_ptr,
      arg,
#if OFFSCREENCANVAS_SUPPORT
      moduleCanvasId,
      offscreenCanvases,
#endif
      transferList,
    };

    if (ENVIRONMENT_IS_PTHREAD) {
      // The prepopulated pool of web workers that can host pthreads is stored
      // in the main JS thread. Therefore if a pthread is attempting to spawn a
      // new thread, the thread creation must be deferred to the main JS thread.
      threadParams.cmd = 'spawnThread';
      postMessage(threadParams, transferList);
      // When we defer thread creation this way, we have no way to detect thread
      // creation synchronously today, so we have to assume success and return 0.
      return 0;
    }

    // We are the main thread, so we have the pthread warmup pool in this
    // thread and can fire off JS thread creation directly ourselves.
    return spawnThread(threadParams);
  },

  emscripten_check_blocking_allowed__deps: ['$warnOnce'],
  emscripten_check_blocking_allowed: function() {
#if (ASSERTIONS || !ALLOW_BLOCKING_ON_MAIN_THREAD) && !MINIMAL_RUNTIME
#if ENVIRONMENT_MAY_BE_NODE
    if (ENVIRONMENT_IS_NODE) return;
#endif

    if (ENVIRONMENT_IS_WORKER) return; // Blocking in a worker/pthread is fine.

    warnOnce('Blocking on the main thread is very dangerous, see https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
#if !ALLOW_BLOCKING_ON_MAIN_THREAD
    abort('Blocking on the main thread is not allowed by default. See https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
#endif

#endif
  },

  __pthread_kill_js: function(thread, signal) {
    if (signal === {{{ cDefs.SIGCANCEL }}}) { // Used by pthread_cancel in musl
      if (!ENVIRONMENT_IS_PTHREAD) cancelThread(thread);
      else postMessage({ 'cmd': 'cancelThread', 'thread': thread });
    } else {
      if (!ENVIRONMENT_IS_PTHREAD) killThread(thread);
      else postMessage({ 'cmd': 'killThread', 'thread': thread });
    }
    return 0;
  },

  // This function is call by a pthread to signal that exit() was called and
  // that the entire process should exit.
  // This function is always called from a pthread, but is executed on the
  // main thread due the __proxy attribute.
  $exitOnMainThread__deps: ['exit',
#if !MINIMAL_RUNTIME
    '$handleException',
#endif
  ],
  $exitOnMainThread__proxy: 'async',
  $exitOnMainThread: function(returnCode) {
#if PTHREADS_DEBUG
    dbg('exitOnMainThread');
#endif
#if PROXY_TO_PTHREAD
    {{{ runtimeKeepalivePop() }}};
#endif
    _exit(returnCode);
  },

  $proxyToMainThread__deps: ['$withStackSave', '_emscripten_run_in_main_runtime_thread_js'],
  $proxyToMainThread__docs: '/** @type{function(number, (number|boolean), ...(number|boolean))} */',
  $proxyToMainThread: function(index, sync) {
    // Additional arguments are passed after those two, which are the actual
    // function arguments.
    // The serialization buffer contains the number of call params, and then
    // all the args here.
    // We also pass 'sync' to C separately, since C needs to look at it.
    var numCallArgs = arguments.length - 2;
    var outerArgs = arguments;
#if ASSERTIONS
    var maxArgs = {{{ cDefs.EM_QUEUED_JS_CALL_MAX_ARGS - 1 }}};
    if (numCallArgs > maxArgs) {
      throw 'proxyToMainThread: Too many arguments ' + numCallArgs + ' to proxied function idx=' + index + ', maximum supported is ' + maxArgs;
    }
#endif
    // Allocate a buffer, which will be copied by the C code.
    return withStackSave(() => {
      // First passed parameter specifies the number of arguments to the function.
      // When BigInt support is enabled, we must handle types in a more complex
      // way, detecting at runtime if a value is a BigInt or not (as we have no
      // type info here). To do that, add a "prefix" before each value that
      // indicates if it is a BigInt, which effectively doubles the number of
      // values we serialize for proxying. TODO: pack this?
      var serializedNumCallArgs = numCallArgs {{{ WASM_BIGINT ? "* 2" : "" }}};
      var args = stackAlloc(serializedNumCallArgs * 8);
      var b = args >> 3;
      for (var i = 0; i < numCallArgs; i++) {
        var arg = outerArgs[2 + i];
#if WASM_BIGINT
        if (typeof arg == 'bigint') {
          // The prefix is non-zero to indicate a bigint.
          HEAP64[b + 2*i] = 1n;
          HEAP64[b + 2*i + 1] = arg;
        } else {
          // The prefix is zero to indicate a JS Number.
          HEAP64[b + 2*i] = 0n;
          HEAPF64[b + 2*i + 1] = arg;
        }
#else
        HEAPF64[b + i] = arg;
#endif
      }
      return __emscripten_run_in_main_runtime_thread_js(index, serializedNumCallArgs, args, sync);
    });
  },

  $emscripten_receive_on_main_thread_js_callArgs: '=[]',

  emscripten_receive_on_main_thread_js__deps: [
    '$proxyToMainThread',
    '$emscripten_receive_on_main_thread_js_callArgs'],
  emscripten_receive_on_main_thread_js: function(index, callingThread, numCallArgs, args) {
    // Sometimes we need to backproxy events to the calling thread (e.g.
    // HTML5 DOM events handlers such as
    // emscripten_set_mousemove_callback()), so keep track in a globally
    // accessible variable about the thread that initiated the proxying.
    PThread.currentProxiedOperationCallerThread = callingThread;
#if WASM_BIGINT
    numCallArgs /= 2;
#endif
    emscripten_receive_on_main_thread_js_callArgs.length = numCallArgs;
    var b = args >> 3;
    for (var i = 0; i < numCallArgs; i++) {
#if WASM_BIGINT
      if (HEAP64[b + 2*i]) {
        // It's a BigInt.
        emscripten_receive_on_main_thread_js_callArgs[i] = HEAP64[b + 2*i + 1];
      } else {
        // It's a Number.
        emscripten_receive_on_main_thread_js_callArgs[i] = HEAPF64[b + 2*i + 1];
      }
#else
      emscripten_receive_on_main_thread_js_callArgs[i] = HEAPF64[b + i];
#endif
    }
    // Proxied JS library funcs are encoded as positive values, and
    // EM_ASMs as negative values (see include_asm_consts)
#if HAVE_EM_ASM
    var isEmAsmConst = index < 0;
    var func = !isEmAsmConst ? proxiedFunctionTable[index] : ASM_CONSTS[-index - 1];
#else
    var func = proxiedFunctionTable[index];
#endif
#if ASSERTIONS
    assert(func.length == numCallArgs, 'Call args mismatch in emscripten_receive_on_main_thread_js');
#endif
    return func.apply(null, emscripten_receive_on_main_thread_js_callArgs);
  },

  $establishStackSpace__internal: true,
  $establishStackSpace: function() {
    var pthread_ptr = _pthread_self();
    var stackHigh = {{{ makeGetValue('pthread_ptr', C_STRUCTS.pthread.stack, 'i32') }}};
    var stackSize = {{{ makeGetValue('pthread_ptr', C_STRUCTS.pthread.stack_size, 'i32') }}};
    var stackLow = stackHigh - stackSize;
#if PTHREADS_DEBUG
    dbg('establishStackSpace: ' + ptrToString(stackHigh) + ' -> ' + ptrToString(stackLow));
#endif
#if ASSERTIONS
    assert(stackHigh != 0);
    assert(stackLow != 0);
    assert(stackHigh > stackLow, 'stackHigh must be higher then stackLow');
#endif
    // Set stack limits used by `emscripten/stack.h` function.  These limits are
    // cached in wasm-side globals to make checks as fast as possible.
    _emscripten_stack_set_limits(stackHigh, stackLow);

#if STACK_OVERFLOW_CHECK >= 2
    setStackLimits();
#endif STACK_OVERFLOW_CHECK

    // Call inside wasm module to set up the stack frame for this pthread in wasm module scope
    stackRestore(stackHigh);

#if STACK_OVERFLOW_CHECK
    // Write the stack cookie last, after we have set up the proper bounds and
    // current position of the stack.
    writeStackCookie();
#endif
  },

  $invokeEntryPoint__deps: ['_emscripten_thread_exit'],
  $invokeEntryPoint: function(ptr, arg) {
#if PTHREADS_DEBUG
    dbg('invokeEntryPoint: ' + ptrToString(ptr));
#endif
#if EXIT_RUNTIME && !MINIMAL_RUNTIME
    // An old thread on this worker may have been canceled without returning the
    // `runtimeKeepaliveCounter` to zero. Reset it now so the new thread won't
    // be affected.
    runtimeKeepaliveCounter = 0;
#endif

#if MAIN_MODULE
    // Before we call the thread entry point, make sure any shared libraries
    // have been loaded on this there.  Otherwise our table migth be not be
    // in sync and might not contain the function pointer `ptr` at all.
    __emscripten_dlsync_self();
#endif
    // pthread entry points are always of signature 'void *ThreadMain(void *arg)'
    // Native codebases sometimes spawn threads with other thread entry point
    // signatures, such as void ThreadMain(void *arg), void *ThreadMain(), or
    // void ThreadMain().  That is not acceptable per C/C++ specification, but
    // x86 compiler ABI extensions enable that to work. If you find the
    // following line to crash, either change the signature to "proper" void
    // *ThreadMain(void *arg) form, or try linking with the Emscripten linker
    // flag -sEMULATE_FUNCTION_POINTER_CASTS to add in emulation for this x86
    // ABI extension.
    var result = {{{ makeDynCall('pp', 'ptr') }}}(arg);
#if STACK_OVERFLOW_CHECK
    checkStackCookie();
#endif
#if MINIMAL_RUNTIME
    // In MINIMAL_RUNTIME the noExitRuntime concept does not apply to
    // pthreads. To exit a pthread with live runtime, use the function
    // emscripten_unwind_to_js_event_loop() in the pthread body.
    __emscripten_thread_exit(result);
#else
    if (keepRuntimeAlive()) {
      PThread.setExitStatus(result);
    } else {
      __emscripten_thread_exit(result);
    }
#endif
  },

#if MAIN_MODULE
  _emscripten_thread_exit_joinable: function(thread) {
    // Called when a thread exits and is joinable.  We mark these threads
    // as finished, which means that are in state where are no longer actually
    // runnning, but remain around waiting to be joined.  In this state they
    // cannot run any more proxied work.
    if (!ENVIRONMENT_IS_PTHREAD) markAsFinshed(thread);
    else postMessage({ 'cmd': 'markAsFinshed', 'thread': thread });
  },

  $markAsFinshed: function(pthread_ptr) {
#if PTHREADS_DEBUG
    dbg('markAsFinshed: ' + ptrToString(pthread_ptr));
#endif
    PThread.finishedThreads.add(pthread_ptr);
    if (pthread_ptr in PThread.outstandingPromises) {
      PThread.outstandingPromises[pthread_ptr].resolve();
    }
  },

  // Asynchronous version dlsync_threads. Always run on the main thread.
  // This work happens asynchronously. The `callback` is called once this work
  // is completed, passing the ctx.
  // TODO(sbc): Should we make a new form of __proxy attribute for JS library
  // function that run asynchronously like but blocks the caller until they are
  // done.  Perhaps "sync_with_ctx"?
  _emscripten_dlsync_threads_async__deps: ['_emscripten_proxy_dlsync_async', 'emscripten_promise_create', '$getPromise'],
  _emscripten_dlsync_threads_async: function(caller, callback, ctx) {
#if PTHREADS_DEBUG
    dbg("_emscripten_dlsync_threads_async caller=" + ptrToString(caller));
#endif
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! _emscripten_dlsync_threads_async() can only ever be called from main thread');
#endif

    const promises = [];
    assert(Object.keys(PThread.outstandingPromises).length === 0);

    // This first promise resolves once the main thread has loaded all modules.
    var info = makePromise();
    promises.push(info.promise);
    __emscripten_dlsync_self_async(info.id);


    // We then create a sequence of promises, one per thread, that resolve once
    // each thread has performed its sync using _emscripten_proxy_dlsync.
    // Any new threads that are created after this call will automaticaly be
    // in sync because we call `__emscripten_dlsync_self` in
    // invokeEntryPoint before the threads entry point is called.
    for (const ptr of Object.keys(PThread.pthreads)) {
      const pthread_ptr = Number(ptr);
      if (pthread_ptr !== caller && !PThread.finishedThreads.has(pthread_ptr)) {
        info = makePromise();
        __emscripten_proxy_dlsync_async(pthread_ptr, info.id);
        PThread.outstandingPromises[pthread_ptr] = info;
        promises.push(info.promise);
      }
    }

#if PTHREADS_DEBUG
    dbg(`_emscripten_dlsync_threads_async: waiting on ${promises.length} promises`);
#endif
    // Once all promises are resolved then we know all threads are in sync and
    // we can call the callback.
    Promise.all(promises).then(() => {
      PThread.outstandingPromises = {};
#if PTHREADS_DEBUG
      dbg('_emscripten_dlsync_threads_async done: calling callback');
#endif
      {{{ makeDynCall('vp', 'callback') }}}(ctx);
    });
  },

  // Synchronous version dlsync_threads. This is only needed for the case then
  // the main thread call dlopen and in that case we have not choice but to
  // synchronously block the main thread until all other threads are in sync.
  // When `dlopen` is called from a worker, the worker itself is blocked but
  // the operation its waiting on (on the main thread) can be async.
  _emscripten_dlsync_threads__deps: ['_emscripten_proxy_dlsync'],
  _emscripten_dlsync_threads: function() {
#if ASSERTIONS
    assert(!ENVIRONMENT_IS_PTHREAD, 'Internal Error! _emscripten_dlsync_threads() can only ever be called from main thread');
#endif
    for (const ptr of Object.keys(PThread.pthreads)) {
      const pthread_ptr = Number(ptr);
      if (!PThread.finishedThreads.has(pthread_ptr)) {
        __emscripten_proxy_dlsync(pthread_ptr);
      }
    }
  },
#endif // MAIN_MODULE

  $checkMailbox__deps: ['$callUserCallback',
                        '_emscripten_thread_mailbox_await'],
  $checkMailbox: function() {
    // Only check the mailbox if we have a live pthread runtime. We implement
    // pthread_self to return 0 if there is no live runtime.
    var pthread_ptr = _pthread_self();
    if (pthread_ptr) {
      // If we are using Atomics.waitAsync as our notification mechanism, wait for
      // a notification before processing the mailbox to avoid missing any work.
      __emscripten_thread_mailbox_await(pthread_ptr);
      callUserCallback(() => __emscripten_check_mailbox());
    }
  },

  _emscripten_thread_mailbox_await__deps: ['$checkMailbox'],
  _emscripten_thread_mailbox_await: function(pthread_ptr) {
    if (typeof Atomics.waitAsync === 'function') {
      // TODO: How to make this work with wasm64?
      var wait = Atomics.waitAsync(HEAP32, pthread_ptr >> 2, pthread_ptr);
#if ASSERTIONS
      assert(wait.async);
#endif
      wait.value.then(checkMailbox);
      var waitingAsync = pthread_ptr + {{{ C_STRUCTS.pthread.waiting_async }}};
      Atomics.store(HEAP32, waitingAsync >> 2, 1);
    }
  },

  _emscripten_notify_mailbox_postmessage__deps: ['$checkMailbox'],
  _emscripten_notify_mailbox_postmessage: function(targetThreadId,
                                                   currThreadId,
                                                   mainThreadId) {
    if (targetThreadId == currThreadId) {
      setTimeout(() => checkMailbox());
    } else if (ENVIRONMENT_IS_PTHREAD) {
      postMessage({'targetThread' : targetThreadId, 'cmd' : 'checkMailbox'});
    } else {
      var worker = PThread.pthreads[targetThreadId];
      if (!worker) {
#if ASSERTIONS
        err('Cannot send message to thread with ID ' + targetThreadId + ', unknown thread ID!');
#endif
        return;
      }
      worker.postMessage({'cmd' : 'checkMailbox'});
    }
  }
};

autoAddDeps(LibraryPThread, '$PThread');
mergeInto(LibraryManager.library, LibraryPThread);