base/message_loop/message_pump_android.cc

// Copyright 2012 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/message_loop/message_pump_android.h"

#include <android/looper.h>
#include <errno.h>
#include <fcntl.h>
#include <jni.h>
#include <sys/eventfd.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <utility>

#include "base/android/jni_android.h"
#include "base/android/scoped_java_ref.h"
#include "base/check_op.h"
#include "base/functional/callback_helpers.h"
#include "base/lazy_instance.h"
#include "base/notreached.h"
#include "base/numerics/safe_conversions.h"
#include "base/run_loop.h"
#include "build/build_config.h"

// Android stripped sys/timerfd.h out of their platform headers, so we have to
// use syscall to make use of timerfd. Once the min API level is 20, we can
// directly use timerfd.h.
#ifndef __NR_timerfd_create
#error "Unable to find syscall for __NR_timerfd_create"
#endif

#ifndef TFD_TIMER_ABSTIME
#define TFD_TIMER_ABSTIME (1 << 0)
#endif

using base::android::JavaParamRef;
using base::android::ScopedJavaLocalRef;

namespace base {

namespace {

// See sys/timerfd.h
long timerfd_create(int clockid, int flags) {
  return syscall(__NR_timerfd_create, clockid, flags);
}

// See sys/timerfd.h
long timerfd_settime(int ufc,
                     int flags,
                     const struct itimerspec* utmr,
                     struct itimerspec* otmr) {
  return syscall(__NR_timerfd_settime, ufc, flags, utmr, otmr);
}

// https://crbug.com/873588. The stack may not be aligned when the ALooper calls
// into our code due to the inconsistent ABI on older Android OS versions.
#if defined(ARCH_CPU_X86)
#define STACK_ALIGN __attribute__((force_align_arg_pointer))
#else
#define STACK_ALIGN
#endif

STACK_ALIGN int NonDelayedLooperCallback(int fd, int events, void* data) {
  if (events & ALOOPER_EVENT_HANGUP)
    return 0;

  DCHECK(events & ALOOPER_EVENT_INPUT);
  MessagePumpForUI* pump = reinterpret_cast<MessagePumpForUI*>(data);
  pump->OnNonDelayedLooperCallback();
  return 1;  // continue listening for events
}

STACK_ALIGN int DelayedLooperCallback(int fd, int events, void* data) {
  if (events & ALOOPER_EVENT_HANGUP)
    return 0;

  DCHECK(events & ALOOPER_EVENT_INPUT);
  MessagePumpForUI* pump = reinterpret_cast<MessagePumpForUI*>(data);
  pump->OnDelayedLooperCallback();
  return 1;  // continue listening for events
}

// A bit added to the |non_delayed_fd_| to keep it signaled when we yield to
// native work below.
constexpr uint64_t kTryNativeWorkBeforeIdleBit = uint64_t(1) << 32;
}  // namespace

MessagePumpForUI::MessagePumpForUI()
    : env_(base::android::AttachCurrentThread()) {
  // The Android native ALooper uses epoll to poll our file descriptors and wake
  // us up. We use a simple level-triggered eventfd to signal that non-delayed
  // work is available, and a timerfd to signal when delayed work is ready to
  // be run.
  non_delayed_fd_ = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
  CHECK_NE(non_delayed_fd_, -1);
  DCHECK_EQ(TimeTicks::GetClock(), TimeTicks::Clock::LINUX_CLOCK_MONOTONIC);

  // We can't create the timerfd with TFD_NONBLOCK | TFD_CLOEXEC as we can't
  // include timerfd.h. See comments above on __NR_timerfd_create. It looks like
  // they're just aliases to O_NONBLOCK and O_CLOEXEC anyways, so this should be
  // fine.
  delayed_fd_ = checked_cast<int>(
      timerfd_create(CLOCK_MONOTONIC, O_NONBLOCK | O_CLOEXEC));
  CHECK_NE(delayed_fd_, -1);

  looper_ = ALooper_prepare(0);
  DCHECK(looper_);
  // Add a reference to the looper so it isn't deleted on us.
  ALooper_acquire(looper_);
  ALooper_addFd(looper_, non_delayed_fd_, 0, ALOOPER_EVENT_INPUT,
                &NonDelayedLooperCallback, reinterpret_cast<void*>(this));
  ALooper_addFd(looper_, delayed_fd_, 0, ALOOPER_EVENT_INPUT,
                &DelayedLooperCallback, reinterpret_cast<void*>(this));
}

MessagePumpForUI::~MessagePumpForUI() {
  DCHECK_EQ(ALooper_forThread(), looper_);
  ALooper_removeFd(looper_, non_delayed_fd_);
  ALooper_removeFd(looper_, delayed_fd_);
  ALooper_release(looper_);
  looper_ = nullptr;

  close(non_delayed_fd_);
  close(delayed_fd_);
}

void MessagePumpForUI::OnDelayedLooperCallback() {
  // There may be non-Chromium callbacks on the same ALooper which may have left
  // a pending exception set, and ALooper does not check for this between
  // callbacks. Check here, and if there's already an exception, just skip this
  // iteration without clearing the fd. If the exception ends up being non-fatal
  // then we'll just get called again on the next polling iteration.
  if (base::android::HasException(env_))
    return;

  // ALooper_pollOnce may call this after Quit() if OnNonDelayedLooperCallback()
  // resulted in Quit() in the same round.
  if (ShouldQuit())
    return;

  // Clear the fd.
  uint64_t value;
  long ret = read(delayed_fd_, &value, sizeof(value));

  // TODO(mthiesse): Figure out how it's possible to hit EAGAIN here.
  // According to http://man7.org/linux/man-pages/man2/timerfd_create.2.html
  // EAGAIN only happens if no timer has expired. Also according to the man page
  // poll only returns readable when a timer has expired. So this function will
  // only be called when a timer has expired, but reading reveals no timer has
  // expired...
  // Quit() and ScheduleDelayedWork() are the only other functions that touch
  // the timerfd, and they both run on the same thread as this callback, so
  // there are no obvious timing or multi-threading related issues.
  DPCHECK(ret >= 0 || errno == EAGAIN);
  DoDelayedLooperWork();
}

void MessagePumpForUI::DoDelayedLooperWork() {
  delayed_scheduled_time_.reset();

  Delegate::NextWorkInfo next_work_info = delegate_->DoWork();

  if (ShouldQuit())
    return;

  if (next_work_info.is_immediate()) {
    ScheduleWork();
    return;
  }

  DoIdleWork();
  if (!next_work_info.delayed_run_time.is_max())
    ScheduleDelayedWork(next_work_info);
}

void MessagePumpForUI::OnNonDelayedLooperCallback() {
  // There may be non-Chromium callbacks on the same ALooper which may have left
  // a pending exception set, and ALooper does not check for this between
  // callbacks. Check here, and if there's already an exception, just skip this
  // iteration without clearing the fd. If the exception ends up being non-fatal
  // then we'll just get called again on the next polling iteration.
  if (base::android::HasException(env_))
    return;

  // ALooper_pollOnce may call this after Quit() if OnDelayedLooperCallback()
  // resulted in Quit() in the same round.
  if (ShouldQuit())
    return;

  // We're about to process all the work requested by ScheduleWork().
  // MessagePump users are expected to do their best not to invoke
  // ScheduleWork() again before DoWork() returns a non-immediate
  // NextWorkInfo below. Hence, capturing the file descriptor's value now and
  // resetting its contents to 0 should be okay. The value currently stored
  // should be greater than 0 since work having been scheduled is the reason
  // we're here. See http://man7.org/linux/man-pages/man2/eventfd.2.html
  uint64_t value = 0;
  long ret = read(non_delayed_fd_, &value, sizeof(value));