将同步数据结构与 Windows API 进行比较

本主题将并发运行时提供的同步数据结构的行为与 Windows API 提供的同步数据结构的行为进行比较。

并发运行时提供的同步数据结构遵循协作线程模型。 在协作线程模型中，同步基元显式将其处理资源传递给其他线程。 这与抢占式线程模型不同，其中处理资源由控制调度程序或操作系统转移到其他线程。

critical_section

concurrency::critical_section 类类似于 Windows CRITICAL_SECTION 结构，因为它只能由一个进程的线程使用。 有关 Windows API 中关键部分的详细信息，请参阅关键部分对象。

reader_writer_lock

concurrency::reader_writer_lock 类类似于 Windows 精简读取器/编写器 (SRW) 锁。 下表说明了相似性和差异。

有关 SRW 锁的详细信息，请参阅平台 SDK 中的精简读取器/编写器 (SRW) 锁。

event

concurrency::event 类类似于未命名的 Windows 手动重置事件。 不过，event 对象以协作方式运行，而 Windows 事件以抢占方式运行。 有关 Windows 事件的详细信息，请参阅事件对象。

示例

说明

若要更好地了解 event 类和 Windows 事件之间的区别，请考虑以下示例。 此示例使调度程序最多可以同时创建两个任务，然后调用两个使用 event 类和 Windows 手动重置事件的类似函数。 每个函数首先创建几个等待共享事件发出信号的任务。 然后，每个函数都会转移到正在运行的任务并向事件发出信号。 之后，每个函数等待信号事件。

代码

// event-comparison.cpp
// compile with: /EHsc
#include <windows.h>
#include <concrtrm.h>
#include <ppl.h>
#include <iostream>
#include <sstream>

using namespace concurrency;
using namespace std;

// Demonstrates the usage of cooperative events.
void RunCooperativeEvents()
{
   // An event object.
   event e;

   // Create a task group and execute five tasks that wait for
   // the event to be set.
   task_group tasks;
   for (int i = 0; i < 5; ++i)
   {
      tasks.run([&] {
         // Print a message before waiting on the event.
         wstringstream ss;
         ss << L"\t\tContext " << GetExecutionContextId() 
            << L": waiting on an event." << endl; 
         wcout << ss.str();

         // Wait for the event to be set.
         e.wait();

         // Print a message after the event is set.
         ss = wstringstream();
         ss << L"\t\tContext " << GetExecutionContextId() 
            << L": received the event." << endl; 
         wcout << ss.str();
      });
   }

   // Wait a sufficient amount of time for all tasks to enter 
   // the waiting state.
   Sleep(1000L);

   // Set the event.

   wstringstream ss;
   ss << L"\tSetting the event." << endl; 
   wcout << ss.str();

   e.set();

   // Wait for all tasks to complete.
   tasks.wait();
}

// Demonstrates the usage of preemptive events.
void RunWindowsEvents()
{
   // A Windows event object.
   HANDLE hEvent = CreateEvent(NULL, TRUE, FALSE, TEXT("Windows Event"));

   // Create a task group and execute five tasks that wait for
   // the event to be set.
   task_group tasks;
   for (int i = 0; i < 5; ++i)
   {
      tasks.run([&] {
         // Print a message before waiting on the event.
         wstringstream ss;
         ss << L"\t\tContext " << GetExecutionContextId() 
            << L": waiting on an event." << endl; 
         wcout << ss.str();

         // Wait for the event to be set.
         WaitForSingleObject(hEvent, INFINITE);

         // Print a message after the event is set.
         ss = wstringstream();
         ss << L"\t\tContext " << GetExecutionContextId() 
            << L": received the event." << endl; 
         wcout << ss.str();
      });
   }

   // Wait a sufficient amount of time for all tasks to enter 
   // the waiting state.
   Sleep(1000L);

   // Set the event.

   wstringstream ss;
   ss << L"\tSetting the event." << endl; 
   wcout << ss.str();

   SetEvent(hEvent);

   // Wait for all tasks to complete.
   tasks.wait();

   // Close the event handle.
   CloseHandle(hEvent);
}

int wmain()
{
   // Create a scheduler policy that allows up to two 
   // simultaneous tasks.
   SchedulerPolicy policy(1, MaxConcurrency, 2);

   // Attach the policy to the current scheduler.
   CurrentScheduler::Create(policy);
   
   wcout << L"Cooperative event:" << endl;
   RunCooperativeEvents();

   wcout << L"Windows event:" << endl;
   RunWindowsEvents();
}

注释

此示例产生以下示例输出：

Cooperative event:
    Context 0: waiting on an event.
    Context 1: waiting on an event.
    Context 2: waiting on an event.
    Context 3: waiting on an event.
    Context 4: waiting on an event.
    Setting the event.
    Context 5: received the event.
    Context 6: received the event.
    Context 7: received the event.
    Context 8: received the event.
    Context 9: received the event.
Windows event:
    Context 10: waiting on an event.
    Context 11: waiting on an event.
    Setting the event.
    Context 12: received the event.
    Context 14: waiting on an event.
    Context 15: received the event.
    Context 16: waiting on an event.
    Context 17: received the event.
    Context 18: waiting on an event.
    Context 19: received the event.
    Context 13: received the event.

由于 event 类以协作方式运行，因此当事件等待进入信号状态时，调度程序可以将处理资源重新分配给另一个上下文。 因此，更多的工作将由使用 event 类的版本完成。 在使用 Windows 事件的版本中，每个等待任务必须在下一个任务开始之前进入信号状态。

有关任务的详细信息，请参阅任务并行。

另请参阅

同步数据结构