Fix relative time in pthreads [v2]

AUTHORS

@@ -443,4 +443,5 @@ a license to everyone to use it as detailed in LICENSE.)
 * John Granström <granstrom.john@gmail.com>
 * Clemens Backes <clemensb@google.com> (copyright owned by Google, Inc.)
 * Tibor Klajnscek <tiborkl@numfum.com>
-* Benjamin Golinvaux <benjamin@golinvaux.com>
+* Benjamin Golinvaux <benjamin@golinvaux.com>
+* Niklas Fiekas <niklas.fiekas@backscattering.de>

src/library.js

@@ -4020,7 +4020,7 @@ LibraryManager.library = {
 #if USE_PTHREADS
 // Pthreads need their clocks synchronized to the execution of the main thread, so give them a special form of the function.
                                "if (ENVIRONMENT_IS_PTHREAD) {\n" +
-                               "  _emscripten_get_now = function() { return performance['now']() - __performance_now_clock_drift; };\n" +
+                               "  _emscripten_get_now = function() { return performance['now']() - Module['__performance_now_clock_drift']; };\n" +
                                "} else " +
 #endif
 #if ENVIRONMENT_MAY_BE_SHELL

src/preamble.js

@@ -67,7 +67,6 @@ var wasmModule;
 // to avoid accessing the global scope.
 var threadInfoStruct = 0;
 var selfThreadId = 0;
-var __performance_now_clock_drift = 0;
 #if WASM_BACKEND
 var tempDoublePtr = 0;
 #endif

src/shell_pthreads.js

@@ -7,10 +7,10 @@
 var ENVIRONMENT_IS_PTHREAD = Module['ENVIRONMENT_IS_PTHREAD'] || false;
 if (ENVIRONMENT_IS_PTHREAD) {
   // Grab imports from the pthread to local scope.
-  buffer = {{{EXPORT_NAME}}}['buffer'];
-  tempDoublePtr = {{{EXPORT_NAME}}}['tempDoublePtr'];
-  DYNAMIC_BASE = {{{EXPORT_NAME}}}['DYNAMIC_BASE'];
-  DYNAMICTOP_PTR = {{{EXPORT_NAME}}}['DYNAMICTOP_PTR'];
+  buffer = Module['buffer'];
+  tempDoublePtr = Module['tempDoublePtr'];
+  DYNAMIC_BASE = Module['DYNAMIC_BASE'];
+  DYNAMICTOP_PTR = Module['DYNAMICTOP_PTR'];
   // Note that not all runtime fields are imported above. Values for STACK_BASE, STACKTOP and STACK_MAX are not yet known at worker.js load time.
   // These will be filled in at pthread startup time (the 'run' message for a pthread - pthread start establishes the stack frame)
 }

src/worker.js

@@ -17,12 +17,6 @@ var tempDoublePtr = 0; // A temporary memory area for global float and double ma
 
 var noExitRuntime;
 
-// performance.now() is specced to return a wallclock time in msecs since that Web Worker/main thread launched. However for pthreads this can cause
-// subtle problems in emscripten_get_now() as this essentially would measure time from pthread_create(), meaning that the clocks between each threads
-// would be wildly out of sync. Therefore sync all pthreads to the clock on the main browser thread, so that different threads see a somewhat
-// coherent clock across each of them (+/- 0.1msecs in testing)
-var __performance_now_clock_drift = 0;
-
 // Cannot use console.log or console.error in a web worker, since that would risk a browser deadlock! https://bugzilla.mozilla.org/show_bug.cgi?id=1049091
 // Therefore implement custom logging facility for threads running in a worker, which queue the messages to main thread to print.
 var Module = {};
@@ -155,8 +149,18 @@ this.onmessage = function(e) {
 #endif
     } else if (e.data.cmd === 'objectTransfer') {
       PThread.receiveObjectTransfer(e.data);
-    } else if (e.data.cmd === 'run') { // This worker was idle, and now should start executing its pthread entry point.
-      __performance_now_clock_drift = performance.now() - e.data.time; // Sync up to the clock of the main thread.
+    } else if (e.data.cmd === 'run') {
+      // This worker was idle, and now should start executing its pthread entry
+      // point.
+      // performance.now() is specced to return a wallclock time in msecs since
+      // that Web Worker/main thread launched. However for pthreads this can
+      // cause subtle problems in emscripten_get_now() as this essentially
+      // would measure time from pthread_create(), meaning that the clocks
+      // between each threads would be wildly out of sync. Therefore sync all
+      // pthreads to the clock on the main browser thread, so that different
+      // threads see a somewhat coherent clock across each of them
+      // (+/- 0.1msecs in testing).
+      Module['__performance_now_clock_drift'] = performance.now() - e.data.time;
       threadInfoStruct = e.data.threadInfoStruct;
       Module['__register_pthread_ptr'](threadInfoStruct, /*isMainBrowserThread=*/0, /*isMainRuntimeThread=*/0); // Pass the thread address inside the asm.js scope to store it for fast access that avoids the need for a FFI out.
       selfThreadId = e.data.selfThreadId;

tests/pthread/test_pthread_reltime.cpp

@@ -0,0 +1,82 @@
+// Copyright 2019 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <iostream>
+#include <ctime>
+#include <condition_variable>
+#include <pthread.h>
+#include <emscripten.h>
+
+static long now() {
+    struct timespec time;
+    clock_gettime(CLOCK_MONOTONIC, &time);
+    return time.tv_sec * 1000 + time.tv_nsec / 1000 / 1000;
+}
+
+static long ping, pong;
+
+static std::mutex mutex;
+static std::condition_variable cond_var;
+static bool pong_requested = false;
+
+void *thread_main(void *arg) {
+    std::cout << "running thread ..." << std::endl;
+
+    std::unique_lock<std::mutex> lock(mutex);
+    while (!pong_requested)
+        cond_var.wait(lock);
+    pong = now(); // Measure time in the pthread
+    std::cout << "pong - ping: " << (pong - ping) << std::endl;
+    pong_requested = false;
+    cond_var.notify_one();
+
+    return NULL;
+}
+
+EMSCRIPTEN_KEEPALIVE
+extern "C" int notify() {
+    {
+        std::unique_lock<std::mutex> lock(mutex);
+        std::cout << "notifying ..." << std::endl;
+        ping = now();
+        pong_requested = true;
+        cond_var.notify_one();
+    }
+
+    {
+        std::unique_lock<std::mutex> lock(mutex);
+        while (pong_requested)
+            cond_var.wait(lock);
+        long last = now();
+        std::cout << "last - pong: " << (last - ping) << std::endl;
+
+        // Time measured on a worker should be relative to the main thread,
+        // so that things are basically monotonic.
+        REPORT_RESULT(int(pong >= ping) + 2 * int(last >= pong));
+    }
+
+    return 0;
+}
+
+int main() {
+    std::cout << "running main ..." << std::endl;
+
+    EM_ASM({
+        setTimeout(function() {
+            Module._notify();
+        });
+    });
+
+    pthread_attr_t attr;
+    pthread_attr_init(&attr);
+
+    pthread_t thread;
+    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+    int error = pthread_create(&thread, &attr, thread_main, NULL);
+    if (error)
+        abort();
+
+    return 0;
+}

tests/test_browser.py

@@ -4584,6 +4584,13 @@ def run(emcc_args=[]):
     run(['-s', 'ASSERTIONS=1'])
     run(['-s', 'PROXY_TO_PTHREAD=1'])
 
+  # Tests that time in a pthread is relative to the main thread, so measurements
+  # on different threads are still monotonic, as if checking a single central
+  # clock.
+  @requires_threads
+  def test_pthread_reltime(self):
+    self.btest(path_from_root('tests', 'pthread', 'test_pthread_reltime.cpp'), expected='3', args=['-s', 'USE_PTHREADS=1', '-s', 'PTHREAD_POOL_SIZE=1'])
+
   # Tests that it is possible to load the main .js file of the application manually via a Blob URL, and still use pthreads.
   @requires_threads
   def test_load_js_from_blob_with_pthreads(self):