third_party/WebKit/public/platform/WebScheduler.h

// Copyright 2014 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 WebScheduler_h
#define WebScheduler_h

#include "WebCommon.h"
#include "public/platform/WebPassOwnPtr.h"
#include "public/platform/WebTaskRunner.h"
#include "public/platform/WebThread.h"
#include "public/platform/WebViewScheduler.h"

namespace blink {

class WebTraceLocation;
class WebView;

// This class is used to submit tasks and pass other information from Blink to
// the platform's scheduler.
class BLINK_PLATFORM_EXPORT WebScheduler {
public:
    virtual ~WebScheduler() { }

    // Called to prevent any more pending tasks from running. Must be called on
    // the associated WebThread.
    virtual void shutdown() = 0;

    // Returns true if there is high priority work pending on the associated WebThread
    // and the caller should yield to let the scheduler service that work.
    // Must be called on the associated WebThread.
    virtual bool shouldYieldForHighPriorityWork() = 0;

    // Returns true if a currently running idle task could exceed its deadline
    // without impacting user experience too much. This should only be used if
    // there is a task which cannot be pre-empted and is likely to take longer
    // than the largest expected idle task deadline. It should NOT be polled to
    // check whether more work can be performed on the current idle task after
    // its deadline has expired - post a new idle task for the continuation of
    // the work in this case.
    // Must be called from the associated WebThread.
    virtual bool canExceedIdleDeadlineIfRequired() = 0;

    // Schedule an idle task to run the associated WebThread. For non-critical
    // tasks which may be reordered relative to other task types and may be
    // starved for an arbitrarily long time if no idle time is available.
    // Takes ownership of |IdleTask|. Can be called from any thread.
    virtual void postIdleTask(const WebTraceLocation&, WebThread::IdleTask*) = 0;

    // Like postIdleTask but guarantees that the posted task will not run
    // nested within an already-running task. Posting an idle task as
    // non-nestable may not affect when the task gets run, or it could
    // make it run later than it normally would, but it won't make it
    // run earlier than it normally would.
    virtual void postNonNestableIdleTask(const WebTraceLocation&, WebThread::IdleTask*) = 0;

    // Like postIdleTask but does not run the idle task until after some other
    // task has run. This enables posting of a task which won't stop the Blink
    // main thread from sleeping, but will start running after it wakes up.
    // Takes ownership of |IdleTask|. Can be called from any thread.
    virtual void postIdleTaskAfterWakeup(const WebTraceLocation&, WebThread::IdleTask*) = 0;

    // Returns a WebTaskRunner for loading tasks. Can be called from any thread.
    virtual WebTaskRunner* loadingTaskRunner() = 0;

    // Returns a WebTaskRunner for timer tasks. Can be called from any thread.
    virtual WebTaskRunner* timerTaskRunner() = 0;

    // Creates a new WebViewScheduler for a given WebView. Must be called from
    // the associated WebThread.
    virtual WebPassOwnPtr<WebViewScheduler> createWebViewScheduler(blink::WebView*) = 0;

    // Suspends the timer queue and increments the timer queue suspension count.
    // May only be called from the main thread.
    virtual void suspendTimerQueue() = 0;

    // Decrements the timer queue suspension count and re-enables the timer queue
    // if the suspension count is zero and the current scheduler policy allows it.
    virtual void resumeTimerQueue() = 0;

    // Tells the scheduler that a navigation task is pending.
    // TODO(alexclarke): Long term should this be a task trait?
    virtual void addPendingNavigation() = 0;

    // Tells the scheduler that a navigation task is no longer pending.
    virtual void removePendingNavigation() = 0;

    // Tells the scheduler that an expected navigation was started.
    virtual void onNavigationStarted() = 0;

#ifdef INSIDE_BLINK
    // Helpers for posting bound functions as tasks.
    typedef Function<void(double deadlineSeconds)> IdleTask;

    void postIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);
    void postNonNestableIdleTask(const WebTraceLocation&, PassOwnPtr<IdleTask>);
    void postIdleTaskAfterWakeup(const WebTraceLocation&, PassOwnPtr<IdleTask>);
#endif
};

} // namespace blink

#endif // WebScheduler_h