ppapi/shared_impl/tracked_callback.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ppapi/shared_impl/tracked_callback.h"

#include <memory>

#include "base/bind.h"
#include "base/check.h"
#include "base/compiler_specific.h"
#include "base/location.h"
#include "base/notreached.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_task_runner_handle.h"
#include "ppapi/c/pp_completion_callback.h"
#include "ppapi/c/pp_errors.h"
#include "ppapi/c/ppb_message_loop.h"
#include "ppapi/shared_impl/callback_tracker.h"
#include "ppapi/shared_impl/ppapi_globals.h"
#include "ppapi/shared_impl/ppb_message_loop_shared.h"
#include "ppapi/shared_impl/proxy_lock.h"
#include "ppapi/shared_impl/resource.h"

namespace ppapi {

namespace {

bool IsMainThread() {
  return PpapiGlobals::Get()
      ->GetMainThreadMessageLoop()
      ->BelongsToCurrentThread();
}

int32_t RunCompletionTask(TrackedCallback::CompletionTask completion_task,
                          int32_t result) {
  ProxyLock::AssertAcquired();
  int32_t task_result = std::move(completion_task).Run(result);
  if (result != PP_ERROR_ABORTED)
    result = task_result;
  return result;
}

}  // namespace

// TrackedCallback -------------------------------------------------------------

// Note: don't keep a Resource* since it may go out of scope before us.
TrackedCallback::TrackedCallback(Resource* resource,
                                 const PP_CompletionCallback& callback)
    : is_scheduled_(false),
      resource_id_(resource ? resource->pp_resource() : 0),
      completed_(false),
      aborted_(false),
      callback_(callback),
      target_loop_(PpapiGlobals::Get()->GetCurrentMessageLoop()),
      result_for_blocked_callback_(PP_OK) {
  // Note that target_loop_ may be NULL at this point, if the plugin has not
  // attached a loop to this thread, or if this is an in-process plugin.
  // The Enter class should handle checking this for us.

  // TODO(dmichael): Add tracking at the instance level, for callbacks that only
  // have an instance (e.g. for MouseLock).
  if (resource) {
    tracker_ = PpapiGlobals::Get()->GetCallbackTrackerForInstance(
        resource->pp_instance());
    tracker_->Add(base::WrapRefCounted(this));
  }

  base::Lock* proxy_lock = ProxyLock::Get();
  if (proxy_lock) {
    ProxyLock::AssertAcquired();
    // If the proxy_lock is valid, we're running out-of-process, and locking
    // is enabled.
    if (is_blocking()) {
      // This is a blocking completion callback, so we will need a condition
      // variable for blocking & signalling the calling thread.
      operation_completed_condvar_ =
          std::make_unique<base::ConditionVariable>(&lock_);
    } else {
      // It's a non-blocking callback, so we should have a MessageLoopResource
      // to dispatch to. Note that we don't error check here, though. Later,
      // EnterResource::SetResult will check to make sure the callback is valid
      // and take appropriate action.
    }
  }
}

TrackedCallback::~TrackedCallback() {}

void TrackedCallback::Abort() {
  Run(PP_ERROR_ABORTED);
}

void TrackedCallback::PostAbort() {
  PostRun(PP_ERROR_ABORTED);
}

void TrackedCallback::Run(int32_t result) {
  // Retain ourselves, since SignalBlockingCallback and MarkAsCompleted might
  // otherwise cause |this| to be deleted. Do this before acquiring lock_ so
  // that |this| is definitely valid at the time we release |lock_|.
  scoped_refptr<TrackedCallback> thiz(this);
  base::AutoLock acquire(lock_);
  // Only allow the callback to be run once. Note that this also covers the case
  // where the callback was previously Aborted because its associated Resource
  // went away. The callback may live on for a while because of a reference from
  // a Closure. But when the Closure runs, Run() quietly does nothing, and the
  // callback will go away when all referring Closures go away.
  if (completed_)
    return;
  if (result == PP_ERROR_ABORTED)
    aborted_ = true;

  // Note that this call of Run() may have been scheduled prior to Abort() or
  // PostAbort() being called. If we have been told to Abort, that always
  // trumps a result that was scheduled before, so we should make sure to pass
  // PP_ERROR_ABORTED.
  if (aborted_)
    result = PP_ERROR_ABORTED;

  if (is_blocking()) {
    // This is a blocking callback; signal the condvar to wake up the thread.
    SignalBlockingCallback(result);
  } else {
    // If there's a target_loop_, and we're not on the right thread, we need to
    // post to target_loop_.
    if (target_loop_ &&
        target_loop_.get() != PpapiGlobals::Get()->GetCurrentMessageLoop()) {
      PostRunWithLock(result);
      return;
    }
    // Do this before running the callback in case of reentrancy from running
    // the completion callback.
    MarkAsCompletedWithLock();

    if (completion_task_)
      result = RunCompletionTask(std::move(completion_task_), result);

    {
      base::AutoUnlock release(lock_);
      // Call the callback without lock_ and without the ProxyLock.
      CallWhileUnlocked(PP_RunCompletionCallback, &callback_, result);
    }
  }
}

void TrackedCallback::PostRun(int32_t result) {
  base::AutoLock acquire(lock_);
  PostRunWithLock(result);
}

void TrackedCallback::set_completion_task(CompletionTask completion_task) {
  base::AutoLock acquire(lock_);
  DCHECK(completion_task_.is_null());
  completion_task_ = std::move(completion_task);
}

// static
bool TrackedCallback::IsPending(
    const scoped_refptr<TrackedCallback>& callback) {
  if (!callback)
    return false;
  base::AutoLock acquire(callback->lock_);
  if (callback->aborted_)
    return false;
  return !callback->completed_;
}

// static
bool TrackedCallback::IsScheduledToRun(
    const scoped_refptr<TrackedCallback>& callback) {
  if (!callback)
    return false;
  base::AutoLock acquire(callback->lock_);
  if (callback->aborted_)
    return false;
  return !callback->completed_ && callback->is_scheduled_;
}

int32_t TrackedCallback::BlockUntilComplete() {
  // Note, we are already holding the proxy lock in this method and many others
  // (see ppapi/thunk/enter.cc for where it gets acquired).
  ProxyLock::AssertAcquired();
  base::AutoLock acquire(lock_);

  // It doesn't make sense to wait on a non-blocking callback. Furthermore,
  // BlockUntilComplete should never be called for in-process plugins, where
  // blocking callbacks are not supported.
  CHECK(is_blocking() && operation_completed_condvar_);

  // Protect us from being deleted to ensure operation_completed_condvar_ is
  // available to wait on when we drop our lock.
  scoped_refptr<TrackedCallback> thiz(this);

  // Unlock proxy lock temporarily; We don't want to block whole proxy while
  // we're waiting for the callback
  ProxyLock::Release();

  while (!completed_) {
    operation_completed_condvar_->Wait();
  }

  // Now we need to get ProxyLock back, but because it's used in outer code to
  // maintain lock order we need to release our lock first
  {
    base::AutoUnlock unlock(lock_);
    ProxyLock::Acquire();
  }

  if (completion_task_) {
    result_for_blocked_callback_ = RunCompletionTask(
        std::move(completion_task_), result_for_blocked_callback_);
  }
  return result_for_blocked_callback_;
}

void TrackedCallback::MarkAsCompleted() {
  base::AutoLock acquire(lock_);
  MarkAsCompletedWithLock();
}

void TrackedCallback::MarkAsCompletedWithLock() {
  lock_.AssertAcquired();
  DCHECK(!completed_);

  // We will be removed; maintain a reference to ensure we won't be deleted
  // until we're done.
  scoped_refptr<TrackedCallback> thiz = this;
  completed_ = true;
  // We may not have a valid resource, in which case we're not in the tracker.
  if (resource_id_)
    tracker_->Remove(thiz);
  tracker_.reset();

  // Relax the cross-thread access restriction to non-thread-safe RefCount.
  // |lock_| protects the access to Resource instances.
  base::ScopedAllowCrossThreadRefCountAccess
      allow_cross_thread_ref_count_access;
  target_loop_.reset();
}

void TrackedCallback::PostRunWithLock(int32_t result) {
  lock_.AssertAcquired();
  if (completed_) {
    NOTREACHED();
    return;
  }
  if (result == PP_ERROR_ABORTED)
    aborted_ = true;
  // We might abort when there's already a scheduled callback, but callers
  // should never try to PostRun more than once otherwise.
  DCHECK(result == PP_ERROR_ABORTED || !is_scheduled_);

  if (is_blocking()) {
    // We might not have a MessageLoop to post to, so we must Signal
    // directly.
    SignalBlockingCallback(result);
  } else {
    base::OnceClosure callback_closure(
        RunWhileLocked(base::BindOnce(&TrackedCallback::Run, this, result)));
    if (target_loop_) {
      target_loop_->PostClosure(FROM_HERE, std::move(callback_closure), 0);
    } else {
      // We must be running in-process and on the main thread (the Enter
      // classes protect against having a null target_loop_ otherwise).
      DCHECK(IsMainThread());
      DCHECK(PpapiGlobals::Get()->IsHostGlobals());
      base::ThreadTaskRunnerHandle::Get()->PostTask(
          FROM_HERE, std::move(callback_closure));
    }
  }
  is_scheduled_ = true;
}

void TrackedCallback::SignalBlockingCallback(int32_t result) {
  lock_.AssertAcquired();
  DCHECK(is_blocking());
  if (!operation_completed_condvar_) {
    // If the condition variable is invalid, there are two possibilities. One,
    // we're running in-process, in which case the call should have come in on
    // the main thread and we should have returned PP_ERROR_BLOCKS_MAIN_THREAD
    // well before this. Otherwise, this callback was not created as a
    // blocking callback. Either way, there's some internal error.
    NOTREACHED();
    return;
  }
  result_for_blocked_callback_ = result;
  // Retain ourselves, since MarkAsCompleted will remove us from the
  // tracker. Then MarkAsCompleted before waking up the blocked thread,
  // which could potentially re-enter.
  scoped_refptr<TrackedCallback> thiz(this);
  MarkAsCompletedWithLock();
  // Wake up the blocked thread. See BlockUntilComplete for where the thread
  // Wait()s.
  operation_completed_condvar_->Signal();
}

}  // namespace ppapi