// 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 "base/message_loop/message_pump_glib.h"
#include <fcntl.h>
#include <math.h>
#include <glib.h>
#include "base/logging.h"
#include "base/posix/eintr_wrapper.h"
#include "base/threading/platform_thread.h"
namespace base {
namespace {
// Return a timeout suitable for the glib loop, -1 to block forever,
// 0 to return right away, or a timeout in milliseconds from now.
int GetTimeIntervalMilliseconds(const TimeTicks& from) {
if (from.is_null())
return -1;
// Be careful here. TimeDelta has a precision of microseconds, but we want a
// value in milliseconds. If there are 5.5ms left, should the delay be 5 or
// 6? It should be 6 to avoid executing delayed work too early.
int delay = static_cast<int>(
ceil((from - TimeTicks::Now()).InMillisecondsF()));
// If this value is negative, then we need to run delayed work soon.
return delay < 0 ? 0 : delay;
}
// A brief refresher on GLib:
// GLib sources have four callbacks: Prepare, Check, Dispatch and Finalize.
// On each iteration of the GLib pump, it calls each source's Prepare function.
// This function should return TRUE if it wants GLib to call its Dispatch, and
// FALSE otherwise. It can also set a timeout in this case for the next time
// Prepare should be called again (it may be called sooner).
// After the Prepare calls, GLib does a poll to check for events from the
// system. File descriptors can be attached to the sources. The poll may block
// if none of the Prepare calls returned TRUE. It will block indefinitely, or
// by the minimum time returned by a source in Prepare.
// After the poll, GLib calls Check for each source that returned FALSE
// from Prepare. The return value of Check has the same meaning as for Prepare,
// making Check a second chance to tell GLib we are ready for Dispatch.
// Finally, GLib calls Dispatch for each source that is ready. If Dispatch
// returns FALSE, GLib will destroy the source. Dispatch calls may be recursive
// (i.e., you can call Run from them), but Prepare and Check cannot.
// Finalize is called when the source is destroyed.
// NOTE: It is common for subsytems to want to process pending events while
// doing intensive work, for example the flash plugin. They usually use the
// following pattern (recommended by the GTK docs):
// while (gtk_events_pending()) {
// gtk_main_iteration();
// }
//
// gtk_events_pending just calls g_main_context_pending, which does the
// following:
// - Call prepare on all the sources.
// - Do the poll with a timeout of 0 (not blocking).
// - Call check on all the sources.
// - *Does not* call dispatch on the sources.
// - Return true if any of prepare() or check() returned true.
//
// gtk_main_iteration just calls g_main_context_iteration, which does the whole
// thing, respecting the timeout for the poll (and block, although it is
// expected not to if gtk_events_pending returned true), and call dispatch.
//
// Thus it is important to only return true from prepare or check if we
// actually have events or work to do. We also need to make sure we keep
// internal state consistent so that if prepare/check return true when called
// from gtk_events_pending, they will still return true when called right
// after, from gtk_main_iteration.
//
// For the GLib pump we try to follow the Windows UI pump model:
// - Whenever we receive a wakeup event or the timer for delayed work expires,
// we run DoWork and/or DoDelayedWork. That part will also run in the other
// event pumps.
// - We also run DoWork, DoDelayedWork, and possibly DoIdleWork in the main
// loop, around event handling.
struct WorkSource : public GSource {
MessagePumpGlib* pump;
};
gboolean WorkSourcePrepare(GSource* source,
gint* timeout_ms) {
*timeout_ms = static_cast<WorkSource*>(source)->pump->HandlePrepare();
// We always return FALSE, so that our timeout is honored. If we were
// to return TRUE, the timeout would be considered to be 0 and the poll
// would never block. Once the poll is finished, Check will be called.
return FALSE;
}
gboolean WorkSourceCheck(GSource* source) {
// Only return TRUE if Dispatch should be called.
return static_cast<WorkSource*>(source)->pump->HandleCheck();
}
gboolean WorkSourceDispatch(GSource* source,
GSourceFunc unused_func,
gpointer unused_data) {
static_cast<WorkSource*>(source)->pump->HandleDispatch();
// Always return TRUE so our source stays registered.
return TRUE;
}
// I wish these could be const, but g_source_new wants non-const.
GSourceFuncs WorkSourceFuncs = {
WorkSourcePrepare,
WorkSourceCheck,
WorkSourceDispatch,
NULL
};
} // namespace
struct MessagePumpGlib::RunState {
Delegate* delegate;
MessagePumpDispatcher* dispatcher;
// Used to flag that the current Run() invocation should return ASAP.
bool should_quit;
// Used to count how many Run() invocations are on the stack.
int run_depth;
// This keeps the state of whether the pump got signaled that there was new
// work to be done. Since we eat the message on the wake up pipe as soon as
// we get it, we keep that state here to stay consistent.
bool has_work;
};
MessagePumpGlib::MessagePumpGlib()
: state_(NULL),
context_(g_main_context_default()),
wakeup_gpollfd_(new GPollFD) {
// Create our wakeup pipe, which is used to flag when work was scheduled.
int fds[2];
int ret = pipe(fds);
DCHECK_EQ(ret, 0);
(void)ret; // Prevent warning in release mode.
wakeup_pipe_read_ = fds[0];
wakeup_pipe_write_ = fds[1];
wakeup_gpollfd_->fd = wakeup_pipe_read_;
wakeup_gpollfd_->events = G_IO_IN;
work_source_ = g_source_new(&WorkSourceFuncs, sizeof(WorkSource));
static_cast<WorkSource*>(work_source_)->pump = this;
g_source_add_poll(work_source_, wakeup_gpollfd_.get());
// Use a low priority so that we let other events in the queue go first.
g_source_set_priority(work_source_, G_PRIORITY_DEFAULT_IDLE);
// This is needed to allow Run calls inside Dispatch.
g_source_set_can_recurse(work_source_, TRUE);
g_source_attach(work_source_, context_);
}
MessagePumpGlib::~MessagePumpGlib() {
g_source_destroy(work_source_);
g_source_unref(work_source_);
close(wakeup_pipe_read_);
close(wakeup_pipe_write_);
}
void MessagePumpGlib::RunWithDispatcher(Delegate* delegate,
MessagePumpDispatcher* dispatcher) {
#ifndef NDEBUG
// Make sure we only run this on one thread. X/GTK only has one message pump
// so we can only have one UI loop per process.
static PlatformThreadId thread_id = PlatformThread::CurrentId();
DCHECK(thread_id == PlatformThread::CurrentId()) <<
"Running MessagePumpGlib on two different threads; "
"this is unsupported by GLib!";
#endif
RunState state;
state.delegate = delegate;
state.dispatcher = dispatcher;
state.should_quit = false;
state.run_depth = state_ ? state_->run_depth + 1 : 1;
state.has_work = false;
RunState* previous_state = state_;
state_ = &state;
// We really only do a single task for each iteration of the loop. If we
// have done something, assume there is likely something more to do. This
// will mean that we don't block on the message pump until there was nothing
// more to do. We also set this to true to make sure not to block on the
// first iteration of the loop, so RunUntilIdle() works correctly.
bool more_work_is_plausible = true;
// We run our own loop instead of using g_main_loop_quit in one of the
// callbacks. This is so we only quit our own loops, and we don't quit
// nested loops run by others. TODO(deanm): Is this what we want?
for (;;) {
// Don't block if we think we have more work to do.
bool block = !more_work_is_plausible;
more_work_is_plausible = g_main_context_iteration(context_, block);
if (state_->should_quit)
break;
more_work_is_plausible |= state_->delegate->DoWork();
if (state_->should_quit)
break;
more_work_is_plausible |=
state_->delegate->DoDelayedWork(&delayed_work_time_);
if (state_->should_quit)
break;
if (more_work_is_plausible)
continue;
more_work_is_plausible = state_->delegate->DoIdleWork();
if (state_->should_quit)
break;
}
state_ = previous_state;
}
// Return the timeout we want passed to poll.
int MessagePumpGlib::HandlePrepare() {
// We know we have work, but we haven't called HandleDispatch yet. Don't let
// the pump block so that we can do some processing.
if (state_ && // state_ may be null during tests.
state_->has_work)
return 0;
// We don't think we have work to do, but make sure not to block
// longer than the next time we need to run delayed work.
return GetTimeIntervalMilliseconds(delayed_work_time_);
}
bool MessagePumpGlib::HandleCheck() {
if (!state_) // state_ may be null during tests.
return false;
// We usually have a single message on the wakeup pipe, since we are only
// signaled when the queue went from empty to non-empty, but there can be
// two messages if a task posted a task, hence we read at most two bytes.
// The glib poll will tell us whether there was data, so this read
// shouldn't block.
if (wakeup_gpollfd_->revents & G_IO_IN) {
char msg[2];
const int num_bytes = HANDLE_EINTR(read(wakeup_pipe_read_, msg, 2));
if (num_bytes < 1) {
NOTREACHED() << "Error reading from the wakeup pipe.";
}
DCHECK((num_bytes == 1 && msg[0] == '!') ||
(num_bytes == 2 && msg[0] == '!' && msg[1] == '!'));
// Since we ate the message, we need to record that we have more work,
// because HandleCheck() may be called without HandleDispatch being called
// afterwards.
state_->has_work = true;
}
if (state_->has_work)
return true;
if (GetTimeIntervalMilliseconds(delayed_work_time_) == 0) {
// The timer has expired. That condition will stay true until we process
// that delayed work, so we don't need to record this differently.
return true;
}
return false;
}
void MessagePumpGlib::HandleDispatch() {
state_->has_work = false;
if (state_->delegate->DoWork()) {
// NOTE: on Windows at this point we would call ScheduleWork (see
// MessagePumpGlib::HandleWorkMessage in message_pump_win.cc). But here,
// instead of posting a message on the wakeup pipe, we can avoid the
// syscalls and just signal that we have more work.
state_->has_work = true;
}
if (state_->should_quit)
return;
state_->delegate->DoDelayedWork(&delayed_work_time_);
}
void MessagePumpGlib::Run(Delegate* delegate) {
RunWithDispatcher(delegate, NULL);
}
void MessagePumpGlib::Quit() {
if (state_) {
state_->should_quit = true;
} else {
NOTREACHED() << "Quit called outside Run!";
}
}
void MessagePumpGlib::ScheduleWork() {
// This can be called on any thread, so we don't want to touch any state
// variables as we would then need locks all over. This ensures that if
// we are sleeping in a poll that we will wake up.
char msg = '!';
if (HANDLE_EINTR(write(wakeup_pipe_write_, &msg, 1)) != 1) {
NOTREACHED() << "Could not write to the UI message loop wakeup pipe!";
}
}
void MessagePumpGlib::ScheduleDelayedWork(const TimeTicks& delayed_work_time) {
// We need to wake up the loop in case the poll timeout needs to be
// adjusted. This will cause us to try to do work, but that's ok.
delayed_work_time_ = delayed_work_time;
ScheduleWork();
}
MessagePumpDispatcher* MessagePumpGlib::GetDispatcher() {
return state_ ? state_->dispatcher : NULL;
}
bool MessagePumpGlib::ShouldQuit() const {
CHECK(state_);
return state_->should_quit;
}
} // namespace base