ios/web/public/web_thread.h - chromium/src - Git at Google

 // 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 IOS_WEB_PUBLIC_WEB_THREAD_H_
 #define IOS_WEB_PUBLIC_WEB_THREAD_H_

 #include <string>
 #include <utility>

 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "base/task_runner_util.h"

 namespace base {
 class MessageLoop;
 }

 namespace tracked_objects {
 class Location;
 }

 namespace web {

 class WebThreadDelegate;

 // Use DCHECK_CURRENTLY_ON(WebThread::ID) to assert that a function can only be
 // called on the named WebThread.
 #define DCHECK_CURRENTLY_ON(thread_identifier)              \
   (DCHECK(::web::WebThread::CurrentlyOn(thread_identifier)) \
    << ::web::WebThread::GetDCheckCurrentlyOnErrorMessage(thread_identifier))

 ///////////////////////////////////////////////////////////////////////////////
 // WebThread
 //
 // Utility functions for threads that are known by name. For example, there is
 // one IO thread for the entire process, and various pieces of code find it
 // useful to retrieve a pointer to the IO thread's message loop.
 //
 // Invoke a task by thread ID:
 //
 //   WebThread::PostTask(WebThread::IO, FROM_HERE, task);
 //
 // The return value is false if the task couldn't be posted because the target
 // thread doesn't exist.  If this could lead to data loss, you need to check the
 // result and restructure the code to ensure it doesn't occur.
 //
 // This class automatically handles the lifetime of different threads.
 // It's always safe to call PostTask on any thread.  If it's not yet created,
 // the task is deleted.  There are no race conditions.  If the thread that the
 // task is posted to is guaranteed to outlive the current thread, then no locks
 // are used.  You should never need to cache pointers to MessageLoops, since
 // they're not thread safe.
 class WebThread {
  public:
   // An enumeration of the well-known threads.
   // NOTE: threads must be listed in the order of their life-time, with each
   // thread outliving every other thread below it.
   enum ID {
     // The main thread in the browser.
     UI,

     // This is the thread that interacts with the database.
     DB,

     // This is the thread that interacts with the file system.
     FILE,

     // This is the thread that processes non-blocking IO, i.e. IPC and network.
     // Blocking IO should happen on other threads like DB, FILE,
     // FILE_USER_BLOCKING and CACHE depending on the usage.
     IO,

     // NOTE: do not add new threads here that are only used by a small number of
     // files. Instead you should just use a Thread class and pass its
     // SingleThreadTaskRunner around. Named threads there are only for threads
     // that are used in many places.

     // This identifier does not represent a thread.  Instead it counts the
     // number of well-known threads.  Insert new well-known threads before this
     // identifier.
     ID_COUNT
   };

   // These are the same methods as in message_loop.h, but are guaranteed to
   // either get posted to the MessageLoop if it's still alive, or be deleted
   // otherwise.
   // They return true iff the thread existed and the task was posted.
   static bool PostTask(ID identifier,
                        const tracked_objects::Location& from_here,
                        base::OnceClosure task);
   static bool PostDelayedTask(ID identifier,
                               const tracked_objects::Location& from_here,
                               base::OnceClosure task,
                               base::TimeDelta delay);
   static bool PostNonNestableTask(ID identifier,
                                   const tracked_objects::Location& from_here,
                                   base::OnceClosure task);
   static bool PostNonNestableDelayedTask(
       ID identifier,
       const tracked_objects::Location& from_here,
       base::OnceClosure task,
       base::TimeDelta delay);

   static bool PostTaskAndReply(ID identifier,
                                const tracked_objects::Location& from_here,
                                base::OnceClosure task,
                                base::OnceClosure reply);

   template <typename ReturnType, typename ReplyArgType>
   static bool PostTaskAndReplyWithResult(
       ID identifier,
       const tracked_objects::Location& from_here,
       base::OnceCallback<ReturnType()> task,
       base::OnceCallback<void(ReplyArgType)> reply) {
     scoped_refptr<base::SingleThreadTaskRunner> task_runner =
         GetTaskRunnerForThread(identifier);
     return base::PostTaskAndReplyWithResult(task_runner.get(), from_here,
                                             std::move(task), std::move(reply));
   }

   template <class T>
   static bool DeleteSoon(ID identifier,
                          const tracked_objects::Location& from_here,
                          const T* object) {
     return GetTaskRunnerForThread(identifier)->DeleteSoon(from_here, object);
   }

   // Callable on any thread.  Returns whether the given well-known thread is
   // initialized.
   static bool IsThreadInitialized(ID identifier) WARN_UNUSED_RESULT;

   // Callable on any thread.  Returns whether execution is currently on the
   // given thread.  To DCHECK this, use the DCHECK_CURRENTLY_ON() macro above.
   static bool CurrentlyOn(ID identifier) WARN_UNUSED_RESULT;

   // Callable on any thread.  Returns whether the threads message loop is valid.
   // If this returns false it means the thread is in the process of shutting
   // down.
   static bool IsMessageLoopValid(ID identifier) WARN_UNUSED_RESULT;

   // If the current message loop is one of the known threads, returns true and
   // sets identifier to its ID.
   static bool GetCurrentThreadIdentifier(ID* identifier) WARN_UNUSED_RESULT;

   // Callers can hold on to a refcounted SingleThreadTaskRunner beyond the
   // lifetime of the thread.
   static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
       ID identifier);

   // Sets the delegate for the specified WebThread.
   //
   // Only one delegate may be registered at a time. Delegates may be
   // unregistered by providing a nullptr pointer.
   //
   // If the caller unregisters a delegate before CleanUp has been
   // called, it must perform its own locking to ensure the delegate is
   // not deleted while unregistering.
   static void SetDelegate(ID identifier, WebThreadDelegate* delegate);

   // Returns an appropriate error message for when DCHECK_CURRENTLY_ON() fails.
   static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);

   // Use these templates in conjunction with RefCountedThreadSafe or
   // std::unique_ptr when you want to ensure that an object is deleted on a
   // specific thread. This is needed when an object can hop between threads
   // (i.e. IO -> FILE -> IO), and thread switching delays can mean that the
   // final IO tasks executes before the FILE task's stack unwinds.
   // This would lead to the object destructing on the FILE thread, which often
   // is not what you want (i.e. to unregister from NotificationService, to
   // notify other objects on the creating thread etc).
   template <ID thread>
   struct DeleteOnThread {
     template <typename T>
     static void Destruct(const T* x) {
       if (CurrentlyOn(thread)) {
         delete x;
       } else {
         if (!DeleteSoon(thread, FROM_HERE, x)) {
           // Leaks at shutdown are acceptable under normal circumstances,
           // do not report.
         }
       }
     }
     template <typename T>
     inline void operator()(T* ptr) const {
       enum { type_must_be_complete = sizeof(T) };
       Destruct(ptr);
     }
   };

   // Sample usage with RefCountedThreadSafe:
   // class Foo
   //     : public base::RefCountedThreadSafe<
   //           Foo, web::WebThread::DeleteOnIOThread> {
   //
   // ...
   //  private:
   //   friend struct web::WebThread::DeleteOnThread<web::WebThread::IO>;
   //   friend class base::DeleteHelper<Foo>;
   //
   //   ~Foo();
   //
   // Sample usage with std::unique_ptr:
   // std::unique_ptr<Foo, web::WebThread::DeleteOnIOThread> ptr;
   struct DeleteOnUIThread : public DeleteOnThread<UI> {};
   struct DeleteOnIOThread : public DeleteOnThread<IO> {};
   struct DeleteOnFileThread : public DeleteOnThread<FILE> {};
   struct DeleteOnDBThread : public DeleteOnThread<DB> {};

  private:
   friend class WebThreadImpl;

   WebThread() {}
   DISALLOW_COPY_AND_ASSIGN(WebThread);
 };

 }  // namespace web

 #endif  // IOS_WEB_PUBLIC_WEB_THREAD_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 IOS_WEB_PUBLIC_WEB_THREAD_H_
	#define IOS_WEB_PUBLIC_WEB_THREAD_H_

	#include <string>
	#include <utility>

	#include "base/callback.h"
	#include "base/compiler_specific.h"
	#include "base/location.h"
	#include "base/logging.h"
	#include "base/macros.h"
	#include "base/memory/ref_counted.h"
	#include "base/single_thread_task_runner.h"
	#include "base/task_runner_util.h"

	namespace base {
	class MessageLoop;
	}

	namespace tracked_objects {
	class Location;
	}

	namespace web {

	class WebThreadDelegate;

	// Use DCHECK_CURRENTLY_ON(WebThread::ID) to assert that a function can only be
	// called on the named WebThread.
	#define DCHECK_CURRENTLY_ON(thread_identifier) \
	(DCHECK(::web::WebThread::CurrentlyOn(thread_identifier)) \
	<< ::web::WebThread::GetDCheckCurrentlyOnErrorMessage(thread_identifier))

	///////////////////////////////////////////////////////////////////////////////
	// WebThread
	//
	// Utility functions for threads that are known by name. For example, there is
	// one IO thread for the entire process, and various pieces of code find it
	// useful to retrieve a pointer to the IO thread's message loop.
	//
	// Invoke a task by thread ID:
	//
	// WebThread::PostTask(WebThread::IO, FROM_HERE, task);
	//
	// The return value is false if the task couldn't be posted because the target
	// thread doesn't exist. If this could lead to data loss, you need to check the
	// result and restructure the code to ensure it doesn't occur.
	//
	// This class automatically handles the lifetime of different threads.
	// It's always safe to call PostTask on any thread. If it's not yet created,
	// the task is deleted. There are no race conditions. If the thread that the
	// task is posted to is guaranteed to outlive the current thread, then no locks
	// are used. You should never need to cache pointers to MessageLoops, since
	// they're not thread safe.
	class WebThread {
	public:
	// An enumeration of the well-known threads.
	// NOTE: threads must be listed in the order of their life-time, with each
	// thread outliving every other thread below it.
	enum ID {
	// The main thread in the browser.
	UI,

	// This is the thread that interacts with the database.
	DB,

	// This is the thread that interacts with the file system.
	FILE,

	// This is the thread that processes non-blocking IO, i.e. IPC and network.
	// Blocking IO should happen on other threads like DB, FILE,
	// FILE_USER_BLOCKING and CACHE depending on the usage.
	IO,

	// NOTE: do not add new threads here that are only used by a small number of
	// files. Instead you should just use a Thread class and pass its
	// SingleThreadTaskRunner around. Named threads there are only for threads
	// that are used in many places.

	// This identifier does not represent a thread. Instead it counts the
	// number of well-known threads. Insert new well-known threads before this
	// identifier.
	ID_COUNT
	};

	// These are the same methods as in message_loop.h, but are guaranteed to
	// either get posted to the MessageLoop if it's still alive, or be deleted
	// otherwise.
	// They return true iff the thread existed and the task was posted.
	static bool PostTask(ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceClosure task);
	static bool PostDelayedTask(ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceClosure task,
	base::TimeDelta delay);
	static bool PostNonNestableTask(ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceClosure task);
	static bool PostNonNestableDelayedTask(
	ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceClosure task,
	base::TimeDelta delay);

	static bool PostTaskAndReply(ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceClosure task,
	base::OnceClosure reply);

	template <typename ReturnType, typename ReplyArgType>
	static bool PostTaskAndReplyWithResult(
	ID identifier,
	const tracked_objects::Location& from_here,
	base::OnceCallback<ReturnType()> task,
	base::OnceCallback<void(ReplyArgType)> reply) {
	scoped_refptr<base::SingleThreadTaskRunner> task_runner =
	GetTaskRunnerForThread(identifier);
	return base::PostTaskAndReplyWithResult(task_runner.get(), from_here,
	std::move(task), std::move(reply));
	}

	template <class T>
	static bool DeleteSoon(ID identifier,
	const tracked_objects::Location& from_here,
	const T* object) {
	return GetTaskRunnerForThread(identifier)->DeleteSoon(from_here, object);
	}

	// Callable on any thread. Returns whether the given well-known thread is
	// initialized.
	static bool IsThreadInitialized(ID identifier) WARN_UNUSED_RESULT;

	// Callable on any thread. Returns whether execution is currently on the
	// given thread. To DCHECK this, use the DCHECK_CURRENTLY_ON() macro above.
	static bool CurrentlyOn(ID identifier) WARN_UNUSED_RESULT;

	// Callable on any thread. Returns whether the threads message loop is valid.
	// If this returns false it means the thread is in the process of shutting
	// down.
	static bool IsMessageLoopValid(ID identifier) WARN_UNUSED_RESULT;

	// If the current message loop is one of the known threads, returns true and
	// sets identifier to its ID.
	static bool GetCurrentThreadIdentifier(ID* identifier) WARN_UNUSED_RESULT;

	// Callers can hold on to a refcounted SingleThreadTaskRunner beyond the
	// lifetime of the thread.
	static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunnerForThread(
	ID identifier);

	// Sets the delegate for the specified WebThread.
	//
	// Only one delegate may be registered at a time. Delegates may be
	// unregistered by providing a nullptr pointer.
	//
	// If the caller unregisters a delegate before CleanUp has been
	// called, it must perform its own locking to ensure the delegate is
	// not deleted while unregistering.
	static void SetDelegate(ID identifier, WebThreadDelegate* delegate);

	// Returns an appropriate error message for when DCHECK_CURRENTLY_ON() fails.
	static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);

	// Use these templates in conjunction with RefCountedThreadSafe or
	// std::unique_ptr when you want to ensure that an object is deleted on a
	// specific thread. This is needed when an object can hop between threads
	// (i.e. IO -> FILE -> IO), and thread switching delays can mean that the
	// final IO tasks executes before the FILE task's stack unwinds.
	// This would lead to the object destructing on the FILE thread, which often
	// is not what you want (i.e. to unregister from NotificationService, to
	// notify other objects on the creating thread etc).
	template <ID thread>
	struct DeleteOnThread {
	template <typename T>
	static void Destruct(const T* x) {
	if (CurrentlyOn(thread)) {
	delete x;
	} else {
	if (!DeleteSoon(thread, FROM_HERE, x)) {
	// Leaks at shutdown are acceptable under normal circumstances,
	// do not report.
	}
	}
	}
	template <typename T>
	inline void operator()(T* ptr) const {
	enum { type_must_be_complete = sizeof(T) };
	Destruct(ptr);
	}
	};

	// Sample usage with RefCountedThreadSafe:
	// class Foo
	// : public base::RefCountedThreadSafe<
	// Foo, web::WebThread::DeleteOnIOThread> {
	//
	// ...
	// private:
	// friend struct web::WebThread::DeleteOnThread<web::WebThread::IO>;
	// friend class base::DeleteHelper<Foo>;
	//
	// ~Foo();
	//
	// Sample usage with std::unique_ptr:
	// std::unique_ptr<Foo, web::WebThread::DeleteOnIOThread> ptr;
	struct DeleteOnUIThread : public DeleteOnThread<UI> {};
	struct DeleteOnIOThread : public DeleteOnThread<IO> {};
	struct DeleteOnFileThread : public DeleteOnThread<FILE> {};
	struct DeleteOnDBThread : public DeleteOnThread<DB> {};

	private:
	friend class WebThreadImpl;

	WebThread() {}
	DISALLOW_COPY_AND_ASSIGN(WebThread);
	};

	} // namespace web

	#endif // IOS_WEB_PUBLIC_WEB_THREAD_H_