tor-browser

InternalThreadPool.cpp (9905B)

---

/* -*- 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/. */

#include "vm/InternalThreadPool.h"

#include "mozilla/TimeStamp.h"

#include "js/ProfilingCategory.h"
#include "js/ProfilingStack.h"
#include "threading/Thread.h"
#include "util/NativeStack.h"
#include "vm/HelperThreadState.h"
#include "vm/JSContext.h"

// We want our default stack size limit to be approximately 2MB, to be safe, but
// expect most threads to use much less. On Linux, however, requesting a stack
// of 2MB or larger risks the kernel allocating an entire 2MB huge page for it
// on first access, which we do not want. To avoid this possibility, we subtract
// 2 standard VM page sizes from our default.
static const uint32_t kDefaultHelperStackSize = 2048 * 1024 - 2 * 4096;

// TSan enforces a minimum stack size that's just slightly larger than our
// default helper stack size.  It does this to store blobs of TSan-specific
// data on each thread's stack.  Unfortunately, that means that even though
// we'll actually receive a larger stack than we requested, the effective
// usable space of that stack is significantly less than what we expect.
// To offset TSan stealing our stack space from underneath us, double the
// default.
//
// Note that we don't need this for ASan/MOZ_ASAN because ASan doesn't
// require all the thread-specific state that TSan does.
#if defined(MOZ_TSAN)
static const uint32_t HELPER_STACK_SIZE = 2 * kDefaultHelperStackSize;
#else
static const uint32_t HELPER_STACK_SIZE = kDefaultHelperStackSize;
#endif

// These macros are identical in function to the same-named ones in
// GeckoProfiler.h, but they are defined separately because SpiderMonkey can't
// use GeckoProfiler.h.
#define PROFILER_RAII_PASTE(id, line) id##line
#define PROFILER_RAII_EXPAND(id, line) PROFILER_RAII_PASTE(id, line)
#define PROFILER_RAII PROFILER_RAII_EXPAND(raiiObject, __LINE__)
#define AUTO_PROFILER_LABEL(label, categoryPair) \
 HelperThread::AutoProfilerLabel PROFILER_RAII( \
     this, label, JS::ProfilingCategoryPair::categoryPair)

using namespace js;

namespace js {

class HelperThread {
 Thread thread;

 ConditionVariable wakeup;

 HelperThreadLockData<HelperThreadTask*> nextTask;

 /*
  * The profiling thread for this helper thread, which can be used to push
  * and pop label frames.
  * This field being non-null indicates that this thread has been registered
  * and needs to be unregistered at shutdown.
  */
 ProfilingStack* profilingStack = nullptr;

public:
 const uint32_t id;

 explicit HelperThread(uint32_t id);
 [[nodiscard]] bool init(InternalThreadPool* pool);

 ThreadId threadId() { return thread.get_id(); }

 void join();

 static void ThreadMain(InternalThreadPool* pool, HelperThread* helper);
 void threadLoop(InternalThreadPool* pool);

 void ensureRegisteredWithProfiler();
 void unregisterWithProfilerIfNeeded();

 void dispatchTask(HelperThreadTask* task);
 void notify();

private:
 struct AutoProfilerLabel {
   AutoProfilerLabel(HelperThread* helperThread, const char* label,
                     JS::ProfilingCategoryPair categoryPair);
   ~AutoProfilerLabel();

  private:
   ProfilingStack* profilingStack;
 };
};

}  // namespace js

InternalThreadPool* InternalThreadPool::Instance = nullptr;

/* static */ InternalThreadPool& InternalThreadPool::Get() {
 MOZ_ASSERT(IsInitialized());
 return *Instance;
}

/* static */
bool InternalThreadPool::Initialize(size_t threadCount,
                                   AutoLockHelperThreadState& lock) {
 if (IsInitialized()) {
   return true;
 }

 auto instance = MakeUnique<InternalThreadPool>();
 if (!instance) {
   return false;
 }

 if (!instance->ensureThreadCount(threadCount, lock)) {
   instance->shutDown(lock);
   return false;
 }

 Instance = instance.release();
 HelperThreadState().setDispatchTaskCallback(DispatchTask, threadCount,
                                             HELPER_STACK_SIZE, lock);
 return true;
}

bool InternalThreadPool::ensureThreadCount(size_t threadCount,
                                          AutoLockHelperThreadState& lock) {
 // Ensure space in freeThreadSet.
 threadCount = std::min(threadCount, sizeof(uint32_t) * CHAR_BIT);

 MOZ_ASSERT(threads(lock).length() <= threadCount);

 if (!threads(lock).reserve(threadCount)) {
   return false;
 }

 while (threads(lock).length() < threadCount) {
   uint32_t id = threads(lock).length();

   auto thread = js::MakeUnique<HelperThread>(id);
   if (!thread || !thread->init(this)) {
     return false;
   }

   threads(lock).infallibleEmplaceBack(std::move(thread));

   setThreadFree(id);
 }

 for (size_t i = 0; i < threads(lock).length(); i++) {
   MOZ_ASSERT(threads(lock)[i]->id == i);
 }

 return true;
}

size_t InternalThreadPool::threadCount(const AutoLockHelperThreadState& lock) {
 return threads(lock).length();
}

/* static */
void InternalThreadPool::ShutDown(AutoLockHelperThreadState& lock) {
 MOZ_ASSERT(HelperThreadState().isTerminating(lock));

 Get().shutDown(lock);
 js_delete(Instance);
 Instance = nullptr;
}

void InternalThreadPool::shutDown(AutoLockHelperThreadState& lock) {
 MOZ_ASSERT(!terminating);
 terminating = true;

 for (auto& thread : threads(lock)) {
   thread->notify();
 }

 for (auto& thread : threads(lock)) {
   AutoUnlockHelperThreadState unlock(lock);
   thread->join();
 }
}

inline HelperThreadVector& InternalThreadPool::threads(
   const AutoLockHelperThreadState& lock) {
 return threads_.ref();
}
inline const HelperThreadVector& InternalThreadPool::threads(
   const AutoLockHelperThreadState& lock) const {
 return threads_.ref();
}

size_t InternalThreadPool::sizeOfIncludingThis(
   mozilla::MallocSizeOf mallocSizeOf,
   const AutoLockHelperThreadState& lock) const {
 return sizeof(InternalThreadPool) +
        threads(lock).sizeOfExcludingThis(mallocSizeOf);
}

/* static */
void InternalThreadPool::DispatchTask(HelperThreadTask* task) {
 Get().dispatchOrQueueTask(task);
}

void InternalThreadPool::dispatchOrQueueTask(HelperThreadTask* task) {
 // This could now use a separate mutex like TaskController, but continues to
 // use the helper thread state lock for convenience.
 AutoLockHelperThreadState lock;
 MOZ_ASSERT(!terminating);
 MOZ_ASSERT(freeThreadSet != 0);

 uint32_t id = mozilla::CountTrailingZeroes32(freeThreadSet);
 clearThreadFree(id);

 HelperThread* thread = threads_.ref()[id].get();
 thread->dispatchTask(task);
}

void InternalThreadPool::setThreadFree(uint32_t threadId) {
 uint32_t idMask = 1 << threadId;
 MOZ_ASSERT((freeThreadSet & idMask) == 0);
 freeThreadSet |= idMask;
}

void InternalThreadPool::clearThreadFree(uint32_t threadId) {
 uint32_t idMask = 1 << threadId;
 MOZ_ASSERT((freeThreadSet & idMask) != 0);
 freeThreadSet &= ~idMask;
}

HelperThread::HelperThread(uint32_t id)
   : thread(Thread::Options().setStackSize(HELPER_STACK_SIZE)), id(id) {}

bool HelperThread::init(InternalThreadPool* pool) {
 return thread.init(HelperThread::ThreadMain, pool, this);
}

void HelperThread::join() { thread.join(); }

/* static */
void HelperThread::ThreadMain(InternalThreadPool* pool, HelperThread* helper) {
 ThisThread::SetName("JS Helper");

 helper->ensureRegisteredWithProfiler();
 helper->threadLoop(pool);
 helper->unregisterWithProfilerIfNeeded();
}

void HelperThread::ensureRegisteredWithProfiler() {
 if (profilingStack) {
   return;
 }

 // Note: To avoid dead locks, we should not hold on the helper thread lock
 // while calling this function. This is safe because the registerThread field
 // is a WriteOnceData<> type stored on the global helper tread state.
 JS::RegisterThreadCallback callback = HelperThreadState().registerThread;
 if (callback) {
   profilingStack =
       callback("JS Helper", reinterpret_cast<void*>(GetNativeStackBase()));
 }
}

void HelperThread::unregisterWithProfilerIfNeeded() {
 if (!profilingStack) {
   return;
 }

 // Note: To avoid dead locks, we should not hold on the helper thread lock
 // while calling this function. This is safe because the unregisterThread
 // field is a WriteOnceData<> type stored on the global helper tread state.
 JS::UnregisterThreadCallback callback = HelperThreadState().unregisterThread;
 if (callback) {
   callback();
   profilingStack = nullptr;
 }
}

HelperThread::AutoProfilerLabel::AutoProfilerLabel(
   HelperThread* helperThread, const char* label,
   JS::ProfilingCategoryPair categoryPair)
   : profilingStack(helperThread->profilingStack) {
 if (profilingStack) {
   profilingStack->pushLabelFrame(label, nullptr, this, categoryPair);
 }
}

HelperThread::AutoProfilerLabel::~AutoProfilerLabel() {
 if (profilingStack) {
   profilingStack->pop();
 }
}

void HelperThread::dispatchTask(HelperThreadTask* task) {
 MOZ_ASSERT(!nextTask);
 nextTask = task;
 notify();
}

void HelperThread::notify() { wakeup.notify_one(); }

void HelperThread::threadLoop(InternalThreadPool* pool) {
 MOZ_ASSERT(CanUseExtraThreads());

 AutoLockHelperThreadState lock;

 while (!pool->terminating) {
   if (!nextTask) {
     AUTO_PROFILER_LABEL("HelperThread::threadLoop::wait", IDLE);
     wakeup.wait(lock);
     continue;
   }

   // JS::RunHelperThreadTask calls runOneTask and then dispatch. Here we split
   // this up so we can mark the current thread as free in between and allow
   // dispatch to pick this thread for the next task.

   HelperThreadState().runOneTask(nextTask, lock);

   nextTask = nullptr;
   pool->setThreadFree(id);

   HelperThreadState().dispatch(lock);
   AutoUnlockHelperThreadState unlock(lock);
 }
}