base/tracing/perfetto_task_runner.cc

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/tracing/perfetto_task_runner.h"

#include <memory>
#include <utility>

#include "base/auto_reset.h"
#include "base/containers/contains.h"
#include "base/functional/bind.h"
#include "base/notreached.h"
#include "base/task/common/checked_lock_impl.h"
#include "base/task/common/scoped_defer_task_posting.h"
#include "base/task/sequenced_task_runner.h"
#include "base/task/thread_pool.h"
#include "base/task/thread_pool/thread_pool_instance.h"
#include "base/tracing/tracing_tls.h"
#include "build/build_config.h"

namespace base::tracing {

PerfettoTaskRunner::PerfettoTaskRunner(
    scoped_refptr<base::SequencedTaskRunner> task_runner,
    bool defer_delayed_tasks)
    : task_runner_(std::move(task_runner)),
      defer_delayed_tasks_(defer_delayed_tasks) {
  CHECK(task_runner_);
}

PerfettoTaskRunner::~PerfettoTaskRunner() {
  DCHECK(task_runner_->RunsTasksInCurrentSequence());
#if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
  fd_controllers_.clear();
#endif  // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
}

void PerfettoTaskRunner::PostTask(std::function<void()> task) {
  PostDelayedTask(task, /* delay_ms */ 0);
}

void PerfettoTaskRunner::PostDelayedTask(std::function<void()> task,
                                         uint32_t delay_ms) {
  if (defer_delayed_tasks_ && delay_ms) {
    deferred_delayed_tasks_.emplace_back(task, delay_ms);
    return;
  }
  base::ScopedDeferTaskPosting::PostOrDefer(
      task_runner_, FROM_HERE,
      base::BindOnce(
          [](std::function<void()> task) {
            // We block any trace events that happens while any
            // Perfetto task is running, or we'll get deadlocks in
            // situations where the StartupTraceWriterRegistry tries
            // to bind a writer which in turn causes a PostTask where
            // a trace event can be emitted, which then deadlocks as
            // it needs a new chunk from the same StartupTraceWriter
            // which we're trying to bind and are keeping the lock
            // to.
            // TODO(oysteine): Try to see if we can be more selective
            // about this.
            const AutoReset<bool> resetter(GetThreadIsInTraceEvent(), true,
                                           false);
            task();
          },
          task),
      base::Milliseconds(delay_ms));
}

bool PerfettoTaskRunner::RunsTasksOnCurrentThread() const {
  DCHECK(task_runner_);
  return task_runner_->RunsTasksInCurrentSequence();
}

// PlatformHandle is an int on POSIX, a HANDLE on Windows.
void PerfettoTaskRunner::AddFileDescriptorWatch(
    perfetto::base::PlatformHandle fd,
    std::function<void()> callback) {
#if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
  DCHECK(task_runner_->RunsTasksInCurrentSequence());
  DCHECK(!base::Contains(fd_controllers_, fd));
  // Set up the |fd| in the map to signal intent to add a watch. We need to
  // PostTask the WatchReadable creation because if we do it in this task we'll
  // race with perfetto setting up the connection on this task and the IO thread
  // setting up epoll on the |fd|. Using a CancelableOnceClosure ensures that
  // the |fd| won't be added for watch if RemoveFileDescriptorWatch is called.
  fd_controllers_[fd].callback.Reset(base::BindOnce(
      [](PerfettoTaskRunner* perfetto_runner, int fd,
         std::function<void()> callback) {
        DCHECK(perfetto_runner->task_runner_->RunsTasksInCurrentSequence());
        // When this callback runs, we must not have removed |fd|'s watch.
        CHECK(base::Contains(perfetto_runner->fd_controllers_, fd));
        auto& controller_and_cb = perfetto_runner->fd_controllers_[fd];
        // We should never overwrite an existing watch.
        CHECK(!controller_and_cb.controller);
        controller_and_cb.controller =
            base::FileDescriptorWatcher::WatchReadable(
                fd, base::BindRepeating(
                        [](std::function<void()> callback) { callback(); },
                        std::move(callback)));
      },
      base::Unretained(this), fd, std::move(callback)));
  task_runner_->PostTask(FROM_HERE, fd_controllers_[fd].callback.callback());
#else   // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
  NOTREACHED();
#endif  // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
}

void PerfettoTaskRunner::RemoveFileDescriptorWatch(
    perfetto::base::PlatformHandle fd) {
#if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
  DCHECK(task_runner_->RunsTasksInCurrentSequence());
  DCHECK(base::Contains(fd_controllers_, fd));
  // This also cancels the base::FileDescriptorWatcher::WatchReadable() task if
  // it's pending.
  fd_controllers_.erase(fd);
#else   // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
  NOTREACHED();
#endif  // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
}

void PerfettoTaskRunner::ResetTaskRunner(
    scoped_refptr<base::SequencedTaskRunner> task_runner) {
  task_runner_ = std::move(task_runner);
  defer_delayed_tasks_ = false;
  for (auto& task : deferred_delayed_tasks_) {
    PostDelayedTask(task.task, task.delay);
  }
  deferred_delayed_tasks_.clear();
}

#if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
PerfettoTaskRunner::FDControllerAndCallback::FDControllerAndCallback() =
    default;

PerfettoTaskRunner::FDControllerAndCallback::~FDControllerAndCallback() =
    default;
#endif  // BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)

PerfettoTaskRunner::DeferredTask::DeferredTask(std::function<void()> task,
                                               uint32_t delay)
    : task(std::move(task)), delay(delay) {}

PerfettoTaskRunner::DeferredTask::DeferredTask(DeferredTask&& task) = default;

PerfettoTaskRunner::DeferredTask::~DeferredTask() = default;

}  // namespace base::tracing