Bug 1704923 - Move helper thread APIs to their own header file r=sfink

This also tidies up the implementation a bit, moving
SetHelperThreadTaskCallback to the JS namespace and removing the unused
RunnableTask class.

Differential Revision: https://phabricator.services.mozilla.com/D116219

js/public/HelperThreadAPI.h

@@ -0,0 +1,31 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * API for supplying an external thread pool to run internal work off the main
+ * thread.
+ */
+
+#ifndef js_HelperThreadAPI_h
+#define js_HelperThreadAPI_h
+
+namespace JS {
+
+/**
+ * Set callback to dispatch a tasks to an external thread pool.
+ *
+ * When the task runs it should call JS::RunHelperThreadTask.
+ */
+using HelperThreadTaskCallback = void (*)();
+extern JS_PUBLIC_API void SetHelperThreadTaskCallback(
+    HelperThreadTaskCallback callback);
+
+// Function to call from external thread pool to run a helper thread task.
+extern JS_PUBLIC_API void RunHelperThreadTask();
+
+}  // namespace JS
+
+#endif  // js_HelperThreadAPI_h

js/public/Utility.h

@@ -69,17 +69,6 @@ enum ThreadType {
   THREAD_TYPE_MAX                    // Used to check shell function arguments
 };
 
-/*
- * Threads need a universal way to dispatch from xpcom thread pools,
- * so having objects inherit from this struct enables
- * mozilla::HelperThreadPool's runnable handler to call runTask() on each type.
- */
-struct RunnableTask {
-  virtual ThreadType threadType() = 0;
-  virtual void runTask() = 0;
-  virtual ~RunnableTask() = default;
-};
-
 namespace oom {
 
 /*

js/src/jsapi.cpp

@@ -1905,15 +1905,6 @@ JS_PUBLIC_API void JS::AssertObjectBelongsToCurrentThread(JSObject* obj) {
   MOZ_RELEASE_ASSERT(CurrentThreadCanAccessRuntime(rt));
 }
 
-// TODO:
-// Bug 1630189: Windows PGO build will have a linking error for
-// HelperThreadTaskCallback, use MOZ_NEVER_INLINE to prevent this. See
-// https://bugzilla.mozilla.org/show_bug.cgi?id=1630189#c4
-JS_PUBLIC_API MOZ_NEVER_INLINE void SetHelperThreadTaskCallback(
-    void (*callback)()) {
-  HelperThreadTaskCallback = callback;
-}
-
 JS_PUBLIC_API void JS::SetFilenameValidationCallback(
     JS::FilenameValidationCallback cb) {
   js::gFilenameValidationCallback = cb;

js/src/jsapi.h

@@ -193,16 +193,6 @@ extern JS_PUBLIC_API bool JS_IsBuiltinEvalFunction(JSFunction* fun);
 /** True iff fun is the Function constructor. */
 extern JS_PUBLIC_API bool JS_IsBuiltinFunctionConstructor(JSFunction* fun);
 
-/**
- * Set callback to send tasks to XPCOM thread pools
- */
-JS_PUBLIC_API void SetHelperThreadTaskCallback(void (*callback)());
-
-namespace JS {
-// Function to call from external thread pool to run a helper thread task.
-extern JS_PUBLIC_API void RunHelperThreadTask();
-}  // namespace JS
-
 extern JS_PUBLIC_API const char* JS_GetImplementationVersion(void);
 
 extern JS_PUBLIC_API void JS_SetWrapObjectCallbacks(

js/src/moz.build

@@ -158,6 +158,7 @@ EXPORTS.js += [
     "../public/GCVector.h",
     "../public/HashTable.h",
     "../public/HeapAPI.h",
+    "../public/HelperThreadAPI.h",
     "../public/Id.h",
     "../public/Initialization.h",
     "../public/JSON.h",

js/src/vm/HelperThreadState.h

@@ -22,6 +22,7 @@
 #include "ds/Fifo.h"
 #include "frontend/CompilationStencil.h"  // CompilationStencil, ExtensibleCompilationStencil, CompilationGCOutput
 #include "js/CompileOptions.h"
+#include "js/HelperThreadAPI.h"
 #include "js/TypeDecls.h"
 #include "threading/ConditionVariable.h"
 #include "threading/Thread.h"
@@ -160,6 +161,11 @@ class GlobalHelperThreadState {
   // This is used to get the HelperThreadTask that are currently running.
   HelperThreadTaskVector helperTasks_;
 
+  // Callback to dispatch a task using an external thread pool. Set by
+  // JS::SetHelperThreadTaskCallback. If this is not set the internal thread
+  // pool is used.
+  JS::HelperThreadTaskCallback dispatchTaskCallback = nullptr;
+
   bool isInitialized_ = false;
 
   bool useInternalThreadPool_;
@@ -199,6 +205,8 @@ class GlobalHelperThreadState {
   void finish();
   void finishThreads();
 
+  void setExternalTaskCallback(JS::HelperThreadTaskCallback callback);
+
   [[nodiscard]] bool ensureContextList(size_t count,
                                        const AutoLockHelperThreadState& lock);
   JSContext* getFirstUnusedContext(AutoLockHelperThreadState& locked);

js/src/vm/HelperThreads.cpp

@@ -21,6 +21,7 @@
 #include "jit/JitRuntime.h"
 #include "js/ContextOptions.h"      // JS::ContextOptions
 #include "js/friend/StackLimits.h"  // js::ReportOverRecursed
+#include "js/HelperThreadAPI.h"
 #include "js/OffThreadScriptCompilation.h"  // JS::OffThreadToken, JS::OffThreadCompileCallback
 #include "js/SourceText.h"
 #include "js/UniquePtr.h"
@@ -133,6 +134,21 @@ void JS::SetProfilingThreadCallbacks(
   HelperThreadState().unregisterThread = unregisterThread;
 }
 
+// Bug 1630189: Without MOZ_NEVER_INLINE, Windows PGO builds have a linking
+// error for HelperThreadTaskCallback.
+JS_PUBLIC_API MOZ_NEVER_INLINE void JS::SetHelperThreadTaskCallback(
+    HelperThreadTaskCallback callback) {
+  HelperThreadState().setExternalTaskCallback(callback);
+}
+
+void GlobalHelperThreadState::setExternalTaskCallback(
+    JS::HelperThreadTaskCallback callback) {
+  AutoLockHelperThreadState lock;
+  MOZ_ASSERT(!isInitialized(lock));
+  MOZ_ASSERT(!dispatchTaskCallback);
+  dispatchTaskCallback = callback;
+}
+
 bool js::StartOffThreadWasmCompile(wasm::CompileTask* task,
                                    wasm::CompileMode mode) {
   return HelperThreadState().submitTask(task, mode);
@@ -1301,7 +1317,7 @@ bool GlobalHelperThreadState::ensureInitialized() {
     return true;
   }
 
-  useInternalThreadPool_ = HelperThreadTaskCallback == nullptr;
+  useInternalThreadPool_ = dispatchTaskCallback == nullptr;
 
   for (size_t& i : runningTaskCount) {
     i = 0;
@@ -1358,6 +1374,8 @@ GlobalHelperThreadState::GlobalHelperThreadState()
       unregisterThread(nullptr),
       wasmTier2GeneratorsFinished_(0),
       useInternalThreadPool_(true) {
+  MOZ_ASSERT(!gHelperThreadState);
+
   cpuCount = ClampDefaultCPUCount(GetCPUCount());
   threadCount = ThreadCountForCPUCount(cpuCount);
   gcParallelThreadCount = threadCount;

js/src/vm/Runtime.cpp

@@ -68,7 +68,6 @@ Atomic<JS::LargeAllocationFailureCallback> js::OnLargeAllocationFailure;
 JS::FilenameValidationCallback js::gFilenameValidationCallback = nullptr;
 
 namespace js {
-void (*HelperThreadTaskCallback)();
 
 #ifndef __wasi__
 bool gCanUseExtraThreads = true;

js/src/vm/Runtime.h

@@ -1181,10 +1181,6 @@ extern mozilla::Atomic<JS::BuildIdOp> GetBuildId;
 
 extern JS::FilenameValidationCallback gFilenameValidationCallback;
 
-// This callback is set by js::SetHelperThreadTaskCallback and may be null.
-// See comment in jsapi.h.
-extern void (*HelperThreadTaskCallback)();
-
 } /* namespace js */
 
 #endif /* vm_Runtime_h */

js/xpconnect/src/XPCJSContext.cpp

@@ -41,6 +41,7 @@
 #include "jsapi.h"
 #include "js/ArrayBuffer.h"
 #include "js/ContextOptions.h"
+#include "js/HelperThreadAPI.h"
 #include "js/Initialization.h"
 #include "js/MemoryMetrics.h"
 #include "js/OffThreadScriptCompilation.h"