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// 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.
#ifndef BASE_RUN_LOOP_H_
#define BASE_RUN_LOOP_H_
#include <utility>
#include <vector>
#include "base/base_export.h"
#include "base/callback.h"
#include "base/containers/stack.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/observer_list.h"
#include "base/sequence_checker.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "build/build_config.h"
namespace base {
#if defined(OS_ANDROID)
class MessagePumpForUI;
#endif
#if defined(OS_IOS)
class MessagePumpUIApplication;
#endif
class SingleThreadTaskRunner;
// Helper class to run the RunLoop::Delegate associated with the current thread.
// A RunLoop::Delegate must have been bound to this thread (ref.
// RunLoop::RegisterDelegateForCurrentThread()) prior to using any of RunLoop's
// member and static methods unless explicitly indicated otherwise (e.g.
// IsRunning/IsNestedOnCurrentThread()). RunLoop::Run can only be called once
// per RunLoop lifetime. Create a RunLoop on the stack and call Run/Quit to run
// a nested RunLoop but please do not use nested loops in production code!
class BASE_EXPORT RunLoop {
public:
// The type of RunLoop: a kDefault RunLoop at the top-level (non-nested) will
// process system and application tasks assigned to its Delegate. When nested
// however a kDefault RunLoop will only process system tasks while a
// kNestableTasksAllowed RunLoop will continue to process application tasks
// even if nested.
//
// This is relevant in the case of recursive RunLoops. Some unwanted run loops
// may occur when using common controls or printer functions. By default,
// recursive task processing is disabled.
//
// In general, nestable RunLoops are to be avoided. They are dangerous and
// difficult to get right, so please use with extreme caution.
//
// A specific example where this makes a difference is:
// - The thread is running a RunLoop.
// - It receives a task #1 and executes it.
// - The task #1 implicitly starts a RunLoop, like a MessageBox in the unit
// test. This can also be StartDoc or GetSaveFileName.
// - The thread receives a task #2 before or while in this second RunLoop.
// - With a kNestableTasksAllowed RunLoop, the task #2 will run right away.
// Otherwise, it will get executed right after task #1 completes in the main
// RunLoop.
enum class Type {
kDefault,
kNestableTasksAllowed,
};
RunLoop(Type type = Type::kDefault);
~RunLoop();
// Run the current RunLoop::Delegate. This blocks until Quit is called. Before
// calling Run, be sure to grab the QuitClosure in order to stop the
// RunLoop::Delegate asynchronously.
void Run();
// Run the current RunLoop::Delegate. This blocks until either |timeout| has
// elapsed or Quit is called. Nesting both with an without timeouts is
// supported. If an inner loop has a longer timeout than the outer loop, the
// outer loop will immediately exit when the inner one does.
void RunWithTimeout(TimeDelta timeout);
// Run the current RunLoop::Delegate until it doesn't find any tasks or
// messages in its queue (it goes idle).
// WARNING #1: This may run long (flakily timeout) and even never return! Do
// not use this when repeating tasks such as animated web pages
// are present.
// WARNING #2: This may return too early! For example, if used to run until an
// incoming event has occurred but that event depends on a task in
// a different queue -- e.g. another TaskRunner or a system event.
// Per the warnings above, this tends to lead to flaky tests; prefer
// QuitClosure()+Run() when at all possible.
void RunUntilIdle();
bool running() const {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
return running_;
}
// Quit() quits an earlier call to Run() immediately. QuitWhenIdle() quits an
// earlier call to Run() when there aren't any tasks or messages in the queue.
//
// These methods are thread-safe but note that Quit() is best-effort when
// called from another thread (will quit soon but tasks that were already
// queued on this RunLoop will get to run first).
//
// There can be other nested RunLoops servicing the same task queue. Quitting
// one RunLoop has no bearing on the others. Quit() and QuitWhenIdle() can be
// called before, during or after Run(). If called before Run(), Run() will
// return immediately when called. Calling Quit() or QuitWhenIdle() after the
// RunLoop has already finished running has no effect.
//
// WARNING: You must NEVER assume that a call to Quit() or QuitWhenIdle() will
// terminate the targetted message loop. If a nested RunLoop continues
// running, the target may NEVER terminate. It is very easy to livelock (run
// forever) in such a case.
void Quit();
void QuitWhenIdle();
// Convenience methods to get a closure that safely calls Quit() or
// QuitWhenIdle() (has no effect if the RunLoop instance is gone).
//
// The resulting Closure is thread-safe (note however that invoking the
// QuitClosure() from another thread than this RunLoop's will result in an
// asynchronous rather than immediate Quit()).
//
// Example:
// RunLoop run_loop;
// PostTask(run_loop.QuitClosure());
// run_loop.Run();
Closure QuitClosure();
Closure QuitWhenIdleClosure();
// Returns true if there is an active RunLoop on this thread.
// Safe to call before RegisterDelegateForCurrentThread().
static bool IsRunningOnCurrentThread();
// Returns true if there is an active RunLoop on this thread and it's nested
// within another active RunLoop.
// Safe to call before RegisterDelegateForCurrentThread().
static bool IsNestedOnCurrentThread();
// A NestingObserver is notified when a nested RunLoop begins and ends.
class BASE_EXPORT NestingObserver {
public:
// Notified before a nested loop starts running work on the current thread.
virtual void OnBeginNestedRunLoop() = 0;
// Notified after a nested loop is done running work on the current thread.
virtual void OnExitNestedRunLoop() {}
protected:
virtual ~NestingObserver() = default;
};
static void AddNestingObserverOnCurrentThread(NestingObserver* observer);
static void RemoveNestingObserverOnCurrentThread(NestingObserver* observer);
// A RunLoop::Delegate is a generic interface that allows RunLoop to be
// separate from the underlying implementation of the message loop for this
// thread. It holds private state used by RunLoops on its associated thread.
// One and only one RunLoop::Delegate must be registered on a given thread
// via RunLoop::RegisterDelegateForCurrentThread() before RunLoop instances
// and RunLoop static methods can be used on it.
class BASE_EXPORT Delegate {
public:
Delegate();
virtual ~Delegate();
// Used by RunLoop to inform its Delegate to Run/Quit. Implementations are
// expected to keep on running synchronously from the Run() call until the
// eventual matching Quit() call or a delay of |timeout| expires. Upon
// receiving a Quit() call or timing out it should return from the Run()
// call as soon as possible without executing remaining tasks/messages.
// Run() calls can nest in which case each Quit() call should result in the
// topmost active Run() call returning. The only other trigger for Run()
// to return is the |should_quit_when_idle_callback_| which the Delegate
// should probe before sleeping when it becomes idle.
// |application_tasks_allowed| is true if this is the first Run() call on
// the stack or it was made from a nested RunLoop of
// Type::kNestableTasksAllowed (otherwise this Run() level should only
// process system tasks).
virtual void Run(bool application_tasks_allowed, TimeDelta timeout) = 0;
virtual void Quit() = 0;
// Invoked right before a RunLoop enters a nested Run() call on this
// Delegate iff this RunLoop is of type kNestableTasksAllowed. The Delegate
// should ensure that the upcoming Run() call will result in processing
// application tasks queued ahead of it without further probing. e.g.
// message pumps on some platforms, like Mac, need an explicit request to
// process application tasks when nested, otherwise they'll only wait for
// system messages.
virtual void EnsureWorkScheduled() = 0;
protected:
// Returns the result of this Delegate's |should_quit_when_idle_callback_|.
// "protected" so it can be invoked only by the Delegate itself.
bool ShouldQuitWhenIdle();
private:
// While the state is owned by the Delegate subclass, only RunLoop can use
// it.
friend class RunLoop;
// A vector-based stack is more memory efficient than the default
// deque-based stack as the active RunLoop stack isn't expected to ever
// have more than a few entries.
using RunLoopStack = stack<RunLoop*, std::vector<RunLoop*>>;
RunLoopStack active_run_loops_;
ObserverList<RunLoop::NestingObserver>::Unchecked nesting_observers_;
#if DCHECK_IS_ON()
bool allow_running_for_testing_ = true;
#endif
// True once this Delegate is bound to a thread via
// RegisterDelegateForCurrentThread().
bool bound_ = false;
// Thread-affine per its use of TLS.
THREAD_CHECKER(bound_thread_checker_);
DISALLOW_COPY_AND_ASSIGN(Delegate);
};
// Registers |delegate| on the current thread. Must be called once and only
// once per thread before using RunLoop methods on it. |delegate| is from then
// on forever bound to that thread (including its destruction).
static void RegisterDelegateForCurrentThread(Delegate* delegate);
// Quits the active RunLoop (when idle) -- there must be one. These were
// introduced as prefered temporary replacements to the long deprecated
// MessageLoop::Quit(WhenIdle)(Closure) methods. Callers should properly plumb
// a reference to the appropriate RunLoop instance (or its QuitClosure)
// instead of using these in order to link Run()/Quit() to a single RunLoop
// instance and increase readability.
static void QuitCurrentDeprecated();
static void QuitCurrentWhenIdleDeprecated();
static Closure QuitCurrentWhenIdleClosureDeprecated();
// Configures all RunLoop::Run() calls on the current thread to run the
// supplied |on_timeout| callback if they run for longer than |timeout|.
//
// Specifying Run() timeouts per-thread avoids the need to cope with Run()s
// executing concurrently with ScopedRunTimeoutForTest initialization or
// teardown, and allows "default" timeouts to be specified by suites, rather
// than explicitly configuring them for every RunLoop, in each test.
//
// Tests can temporarily override any currently-active Run() timeout, e.g. to
// allow a step to Run() for longer than the suite's default timeout, by
// creating a new ScopedRunTimeoutForTest on their stack, e.g:
//
// ScopedRunTimeoutForTest default_timeout(kDefaultRunTimeout, on_timeout);
// ... do other test stuff ...
// RunLoop().Run(); // Run for up to kDefaultRunTimeout.
// ...
// {
// ScopedRunTimeoutForTest specific_timeout(kTestSpecificTimeout, ...);
// RunLoop().Run(); // Run for up to kTestSpecificTimeout.
// }
// ...
// RunLoop().Run(); // Run for up to kDefaultRunTimeout.
//
// The currently-active timeout can also be temporarily disabled:
// ScopedDisableRunTimeoutForTest disable_timeout;
//
// ScopedTaskEnvironment applies a default Run() timeout after which a
// LOG(FATAL) is performed, to dump a crash stack for diagnosis. Tests adding
// their own Run() timeouts can use e.g. MakeExpectedNotRunClosure().
class BASE_EXPORT ScopedRunTimeoutForTest {
public:
ScopedRunTimeoutForTest(TimeDelta timeout, RepeatingClosure on_timeout);
~ScopedRunTimeoutForTest();
// Returns the active ScopedRunTimeoutForTest on the calling thread, if any,
// or null otherwise.
static const RunLoop::ScopedRunTimeoutForTest* Current();
TimeDelta timeout() const { return timeout_; }
const RepeatingClosure& on_timeout() const { return on_timeout_; }
private:
const TimeDelta timeout_;
const RepeatingClosure on_timeout_;
ScopedRunTimeoutForTest* const nested_timeout_;
DISALLOW_COPY_AND_ASSIGN(ScopedRunTimeoutForTest);
};
class BASE_EXPORT ScopedDisableRunTimeoutForTest {
public:
ScopedDisableRunTimeoutForTest();
~ScopedDisableRunTimeoutForTest();
private:
ScopedRunTimeoutForTest* const nested_timeout_;
DISALLOW_COPY_AND_ASSIGN(ScopedDisableRunTimeoutForTest);
};
// Run() will DCHECK if called while there's a ScopedDisallowRunningForTesting
// in scope on its thread. This is useful to add safety to some test
// constructs which allow multiple task runners to share the main thread in
// unit tests. While the main thread can be shared by multiple runners to
// deterministically fake multi threading, there can still only be a single
// RunLoop::Delegate per thread and RunLoop::Run() should only be invoked from
// it (or it would result in incorrectly driving TaskRunner A while in
// TaskRunner B's context).
class BASE_EXPORT ScopedDisallowRunningForTesting {
public:
ScopedDisallowRunningForTesting();
~ScopedDisallowRunningForTesting();
private:
#if DCHECK_IS_ON()
Delegate* current_delegate_;
const bool previous_run_allowance_;
#endif // DCHECK_IS_ON()
DISALLOW_COPY_AND_ASSIGN(ScopedDisallowRunningForTesting);
};
private:
FRIEND_TEST_ALL_PREFIXES(MessageLoopTypedTest, RunLoopQuitOrderAfter);
#if defined(OS_ANDROID)
// Android doesn't support the blocking RunLoop::Run, so it calls
// BeforeRun and AfterRun directly.
friend class MessagePumpForUI;
#endif
#if defined(OS_IOS)
// iOS doesn't support the blocking RunLoop::Run, so it calls
// BeforeRun directly.
friend class MessagePumpUIApplication;
#endif
// Return false to abort the Run.
bool BeforeRun();
void AfterRun();
// A copy of RunLoop::Delegate for the thread driven by tis RunLoop for quick
// access without using TLS (also allows access to state from another sequence
// during Run(), ref. |sequence_checker_| below).
Delegate* delegate_;
const Type type_;
#if DCHECK_IS_ON()
bool run_called_ = false;
#endif
bool quit_called_ = false;
bool running_ = false;
// Used to record that QuitWhenIdle() was called on this RunLoop, meaning that
// the Delegate should quit Run() once it becomes idle (it's responsible for
// probing this state via ShouldQuitWhenIdle()). This state is stored here
// rather than pushed to Delegate to support nested RunLoops.
bool quit_when_idle_received_ = false;
// True if use of QuitCurrent*Deprecated() is allowed. Taking a Quit*Closure()
// from a RunLoop implicitly sets this to false, so QuitCurrent*Deprecated()
// cannot be used while that RunLoop is being Run().
bool allow_quit_current_deprecated_ = true;
// RunLoop is not thread-safe. Its state/methods, unless marked as such, may
// not be accessed from any other sequence than the thread it was constructed
// on. Exception: RunLoop can be safely accessed from one other sequence (or
// single parallel task) during Run() -- e.g. to Quit() without having to
// plumb ThreatTaskRunnerHandle::Get() throughout a test to repost QuitClosure
// to origin thread.
SEQUENCE_CHECKER(sequence_checker_);
const scoped_refptr<SingleThreadTaskRunner> origin_task_runner_;
// WeakPtrFactory for QuitClosure safety.
WeakPtrFactory<RunLoop> weak_factory_;
DISALLOW_COPY_AND_ASSIGN(RunLoop);
};
} // namespace base
#endif // BASE_RUN_LOOP_H_