CSE2410 Fall 2014 Bounce

// Copyright 2008 the V8 project authors. All rights reserved.

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are

// met:

//

//     * Redistributions of source code must retain the above copyright

//       notice, this list of conditions and the following disclaimer.

//     * Redistributions in binary form must reproduce the above

//       copyright notice, this list of conditions and the following

//       disclaimer in the documentation and/or other materials provided

//       with the distribution.

//     * Neither the name of Google Inc. nor the names of its

//       contributors may be used to endorse or promote products derived

//       from this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "v8.h"

#include "api.h"

#include "bootstrapper.h"

#include "debug.h"

#include "execution.h"

#include "v8threads.h"

#include "regexp-stack.h"

namespace v8 {

static internal::Thread::LocalStorageKey thread_state_key =

    internal::Thread::CreateThreadLocalKey();

static internal::Thread::LocalStorageKey thread_id_key =

    internal::Thread::CreateThreadLocalKey();

// Track whether this V8 instance has ever called v8::Locker. This allows the

// API code to verify that the lock is always held when V8 is being entered.

bool Locker::active_ = false;

// Constructor for the Locker object.  Once the Locker is constructed the

// current thread will be guaranteed to have the big V8 lock.

Locker::Locker() : has_lock_(false), top_level_(true) {

  // Record that the Locker has been used at least once.

  active_ = true;

  // Get the big lock if necessary.

  if (!internal::ThreadManager::IsLockedByCurrentThread()) {

    internal::ThreadManager::Lock();

    has_lock_ = true;

    // This may be a locker within an unlocker in which case we have to

    // get the saved state for this thread and restore it.

    if (internal::ThreadManager::RestoreThread()) {

      top_level_ = false;

    }

  }

  ASSERT(internal::ThreadManager::IsLockedByCurrentThread());

  // Make sure this thread is assigned a thread id.

  internal::ThreadManager::AssignId();

}

bool Locker::IsLocked() {

  return internal::ThreadManager::IsLockedByCurrentThread();

}

Locker::~Locker() {

  ASSERT(internal::ThreadManager::IsLockedByCurrentThread());

  if (has_lock_) {

    if (!top_level_) {

      internal::ThreadManager::ArchiveThread();

    }

    internal::ThreadManager::Unlock();

  }

}

Unlocker::Unlocker() {

  ASSERT(internal::ThreadManager::IsLockedByCurrentThread());

  internal::ThreadManager::ArchiveThread();

  internal::ThreadManager::Unlock();

}

Unlocker::~Unlocker() {

  ASSERT(!internal::ThreadManager::IsLockedByCurrentThread());

  internal::ThreadManager::Lock();

  internal::ThreadManager::RestoreThread();

}

void Locker::StartPreemption(int every_n_ms) {

  v8::internal::ContextSwitcher::StartPreemption(every_n_ms);

}

void Locker::StopPreemption() {

  v8::internal::ContextSwitcher::StopPreemption();

}

namespace internal {

bool ThreadManager::RestoreThread() {

  // First check whether the current thread has been 'lazily archived', ie

  // not archived at all.  If that is the case we put the state storage we

  // had prepared back in the free list, since we didn't need it after all.

  if (lazily_archived_thread_.IsSelf()) {

    lazily_archived_thread_.Initialize(ThreadHandle::INVALID);

    ASSERT(Thread::GetThreadLocal(thread_state_key) ==

           lazily_archived_thread_state_);

    lazily_archived_thread_state_->set_id(kInvalidId);

    lazily_archived_thread_state_->LinkInto(ThreadState::FREE_LIST);

    lazily_archived_thread_state_ = NULL;

    Thread::SetThreadLocal(thread_state_key, NULL);

    return true;

  }

  // Make sure that the preemption thread cannot modify the thread state while

  // it is being archived or restored.

  ExecutionAccess access;

  // If there is another thread that was lazily archived then we have to really

  // archive it now.

  if (lazily_archived_thread_.IsValid()) {

    EagerlyArchiveThread();

  }

  ThreadState* state =

      reinterpret_cast<ThreadState*>(Thread::GetThreadLocal(thread_state_key));

  if (state == NULL) {

    return false;

  }

  char* from = state->data();

  from = HandleScopeImplementer::RestoreThread(from);

  from = Top::RestoreThread(from);

  from = Debug::RestoreDebug(from);

  from = StackGuard::RestoreStackGuard(from);

  from = RegExpStack::RestoreStack(from);

  from = Bootstrapper::RestoreState(from);

  Thread::SetThreadLocal(thread_state_key, NULL);

  state->set_id(kInvalidId);

  state->Unlink();

  state->LinkInto(ThreadState::FREE_LIST);

  return true;

}

void ThreadManager::Lock() {

  mutex_->Lock();

  mutex_owner_.Initialize(ThreadHandle::SELF);

  ASSERT(IsLockedByCurrentThread());

}

void ThreadManager::Unlock() {

  mutex_owner_.Initialize(ThreadHandle::INVALID);

  mutex_->Unlock();

}

static int ArchiveSpacePerThread() {

  return HandleScopeImplementer::ArchiveSpacePerThread() +

                            Top::ArchiveSpacePerThread() +

                          Debug::ArchiveSpacePerThread() +

                     StackGuard::ArchiveSpacePerThread() +

                    RegExpStack::ArchiveSpacePerThread() +

                   Bootstrapper::ArchiveSpacePerThread();

}

ThreadState* ThreadState::free_anchor_ = new ThreadState();

ThreadState* ThreadState::in_use_anchor_ = new ThreadState();

ThreadState::ThreadState() : id_(ThreadManager::kInvalidId),

                             next_(this), previous_(this) {

}

void ThreadState::AllocateSpace() {

  data_ = NewArray<char>(ArchiveSpacePerThread());

}

void ThreadState::Unlink() {

  next_->previous_ = previous_;

  previous_->next_ = next_;

}

void ThreadState::LinkInto(List list) {

  ThreadState* flying_anchor =

      list == FREE_LIST ? free_anchor_ : in_use_anchor_;

  next_ = flying_anchor->next_;

  previous_ = flying_anchor;

  flying_anchor->next_ = this;

  next_->previous_ = this;

}

ThreadState* ThreadState::GetFree() {

  ThreadState* gotten = free_anchor_->next_;

  if (gotten == free_anchor_) {

    ThreadState* new_thread_state = new ThreadState();

    new_thread_state->AllocateSpace();

    return new_thread_state;

  }

  return gotten;

}

// Gets the first in the list of archived threads.

ThreadState* ThreadState::FirstInUse() {

  return in_use_anchor_->Next();

}

ThreadState* ThreadState::Next() {

  if (next_ == in_use_anchor_) return NULL;

  return next_;

}

int ThreadManager::next_id_ = 0;

Mutex* ThreadManager::mutex_ = OS::CreateMutex();

ThreadHandle ThreadManager::mutex_owner_(ThreadHandle::INVALID);

ThreadHandle ThreadManager::lazily_archived_thread_(ThreadHandle::INVALID);

ThreadState* ThreadManager::lazily_archived_thread_state_ = NULL;

void ThreadManager::ArchiveThread() {

  ASSERT(!lazily_archived_thread_.IsValid());

  ASSERT(Thread::GetThreadLocal(thread_state_key) == NULL);

  ThreadState* state = ThreadState::GetFree();

  state->Unlink();

  Thread::SetThreadLocal(thread_state_key, reinterpret_cast<void*>(state));

  lazily_archived_thread_.Initialize(ThreadHandle::SELF);

  lazily_archived_thread_state_ = state;

  ASSERT(state->id() == kInvalidId);

  state->set_id(CurrentId());

  ASSERT(state->id() != kInvalidId);

}

void ThreadManager::EagerlyArchiveThread() {

  ThreadState* state = lazily_archived_thread_state_;

  state->LinkInto(ThreadState::IN_USE_LIST);

  char* to = state->data();

  to = HandleScopeImplementer::ArchiveThread(to);

  to = Top::ArchiveThread(to);

  to = Debug::ArchiveDebug(to);

  to = StackGuard::ArchiveStackGuard(to);

  to = RegExpStack::ArchiveStack(to);

  to = Bootstrapper::ArchiveState(to);

  lazily_archived_thread_.Initialize(ThreadHandle::INVALID);

  lazily_archived_thread_state_ = NULL;

}

void ThreadManager::Iterate(ObjectVisitor* v) {

  // Expecting no threads during serialization/deserialization

  for (ThreadState* state = ThreadState::FirstInUse();

       state != NULL;

       state = state->Next()) {

    char* data = state->data();

    data = HandleScopeImplementer::Iterate(v, data);

    data = Top::Iterate(v, data);

  }

}

void ThreadManager::MarkCompactPrologue(bool is_compacting) {

  for (ThreadState* state = ThreadState::FirstInUse();

       state != NULL;

       state = state->Next()) {

    char* data = state->data();

    data += HandleScopeImplementer::ArchiveSpacePerThread();

    Top::MarkCompactPrologue(is_compacting, data);

  }

}

void ThreadManager::MarkCompactEpilogue(bool is_compacting) {

  for (ThreadState* state = ThreadState::FirstInUse();

       state != NULL;

       state = state->Next()) {

    char* data = state->data();

    data += HandleScopeImplementer::ArchiveSpacePerThread();

    Top::MarkCompactEpilogue(is_compacting, data);

  }

}

int ThreadManager::CurrentId() {

  return bit_cast<int, void*>(Thread::GetThreadLocal(thread_id_key));

}

void ThreadManager::AssignId() {

  if (Thread::GetThreadLocal(thread_id_key) == NULL) {

    Thread::SetThreadLocal(thread_id_key, bit_cast<void*, int>(next_id_++));

  }

}

// This is the ContextSwitcher singleton. There is at most a single thread

// running which delivers preemption events to V8 threads.

ContextSwitcher* ContextSwitcher::singleton_ = NULL;

ContextSwitcher::ContextSwitcher(int every_n_ms)

  : keep_going_(true),

    sleep_ms_(every_n_ms) {

}

// Set the scheduling interval of V8 threads. This function starts the

// ContextSwitcher thread if needed.

void ContextSwitcher::StartPreemption(int every_n_ms) {

  ASSERT(Locker::IsLocked());

  if (singleton_ == NULL) {

    // If the ContextSwitcher thread is not running at the moment start it now.

    singleton_ = new ContextSwitcher(every_n_ms);

    singleton_->Start();

  } else {

    // ContextSwitcher thread is already running, so we just change the

    // scheduling interval.

    singleton_->sleep_ms_ = every_n_ms;

  }

}

// Disable preemption of V8 threads. If multiple threads want to use V8 they

// must cooperatively schedule amongst them from this point on.

void ContextSwitcher::StopPreemption() {

  ASSERT(Locker::IsLocked());

  if (singleton_ != NULL) {

    // The ContextSwitcher thread is running. We need to stop it and release

    // its resources.

    singleton_->keep_going_ = false;

    singleton_->Join();  // Wait for the ContextSwitcher thread to exit.

    // Thread has exited, now we can delete it.

    delete(singleton_);

    singleton_ = NULL;

  }

}

// Main loop of the ContextSwitcher thread: Preempt the currently running V8

// thread at regular intervals.

void ContextSwitcher::Run() {

  while (keep_going_) {

    OS::Sleep(sleep_ms_);

    StackGuard::Preempt();

  }

}

// Acknowledge the preemption by the receiving thread.

void ContextSwitcher::PreemptionReceived() {

  ASSERT(Locker::IsLocked());

  // There is currently no accounting being done for this. But could be in the

  // future, which is why we leave this in.

}

}  // namespace internal

}  // namespace v8