如何：创建使用特定计划程序策略的代理

项目
06/16/2023

代理是一个应用程序组件，它与其他组件异步工作以解决大型计算任务。代理通常具有设定的生命周期并维护状态。

每个代理都可以具有独特的应用程序要求。例如，启用用户交互（检索输入或显示输出）的代理可能需要更高优先级的计算资源访问。通过计划程序策略，可控制计划程序在管理任务时使用的策略。本主题演示如何创建使用特定计划程序策略的代理。

有关将自定义计划程序策略与异步消息块一起使用的基本示例，请参阅如何：指定特定的计划程序策略。

本主题使用异步代理库中的功能（如代理、消息块和消息传递函数）来执行工作。有关异步代理库的详细信息，请参阅异步代理库。

示例

下面的示例定义从 concurrency::agent 派生的两个类：permutor 和 printer。 permutor 类计算给定输入字符串的所有排列。 printer 类将进度消息输出到控制台。 permutor 类执行计算密集型操作，该操作可能会使用所有可用的计算资源。为了有用，printer 类必须及时输出每条进度消息。

为了向 printer 类提供对计算资源的公平访问，此示例使用如何：管理计划程序实例中所述的步骤来创建具有自定义策略的计划程序实例。自定义策略将线程优先级指定为最高优先级类。

为了说明使用具有自定义策略的计划程序的好处，此示例执行整个任务两次。本示例首先使用默认计划程序来计划这两个任务。然后，该示例使用默认计划程序来计划 permutor 对象，并使用具有自定义策略的计划程序来计划 printer 对象。

// permute-strings.cpp
// compile with: /EHsc
#include <windows.h>
#include <ppl.h>
#include <agents.h>
#include <iostream>
#include <sstream>

using namespace concurrency;
using namespace std;

// Computes all permutations of a given input string.
class permutor : public agent
{
public:
   explicit permutor(ISource<wstring>& source,
      ITarget<unsigned int>& progress)
      : _source(source)
      , _progress(progress)
   {
   }

   explicit permutor(ISource<wstring>& source,
      ITarget<unsigned int>& progress,
      Scheduler& scheduler)
      : agent(scheduler)
      , _source(source)
      , _progress(progress)
   {
   }

   explicit permutor(ISource<wstring>& source,
      ITarget<unsigned int>& progress,
      ScheduleGroup& group)
      : agent(group)       
      , _source(source)
      , _progress(progress)
   {
   }
   
protected:
   // Performs the work of the agent.
   void run()
   {
      // Read the source string from the buffer.
      wstring s = receive(_source);

      // Compute all permutations.
      permute(s);

      // Set the status of the agent to agent_done.
      done();
   }

   // Computes the factorial of the given value.
   unsigned int factorial(unsigned int n)
   {
      if (n == 0)
         return 0;
      if (n == 1)
         return 1;
      return n * factorial(n - 1);
   }

   // Computes the nth permutation of the given wstring.
   wstring permutation(int n, const wstring& s) 
   {
      wstring t(s);

      size_t len = t.length();
      for (unsigned int i = 2; i < len; ++i)
      {
         swap(t[n % i], t[i]);
         n = n / i;
      }
      return t;
   }

   // Computes all permutations of the given string.
   void permute(const wstring& s)
   {      
      // The factorial gives us the number of permutations.
      unsigned int permutation_count = factorial(s.length());

      // The number of computed permutations.
      LONG count = 0L;      

      // Tracks the previous percentage so that we only send the percentage
      // when it changes.
      unsigned int previous_percent = 0u;

      // Send initial progress message.
      send(_progress, previous_percent);

      // Compute all permutations in parallel.
      parallel_for (0u, permutation_count, [&](unsigned int i) {
         // Compute the permutation.
         permutation(i, s);

         // Send the updated status to the progress reader.
         unsigned int percent = 100 * InterlockedIncrement(&count) / permutation_count;
         if (percent > previous_percent)
         {
             send(_progress, percent);
             previous_percent = percent;
         }
      });

      // Send final progress message.
      send(_progress, 100u);
   }

private:
   // The buffer that contains the source string to permute.
   ISource<wstring>& _source;

   // The buffer to write progress status to.
   ITarget<unsigned int>& _progress;
};

// Prints progress messages to the console.
class printer : public agent
{
public:
   explicit printer(ISource<wstring>& source,
      ISource<unsigned int>& progress)
      : _source(source)
      , _progress(progress)
   {
   }

   explicit printer(ISource<wstring>& source,
      ISource<unsigned int>& progress, Scheduler& scheduler)
      : agent(scheduler)
      , _source(source)
      , _progress(progress)
   {
   }

   explicit printer(ISource<wstring>& source,
      ISource<unsigned int>& progress, ScheduleGroup& group)
      : agent(group)       
      , _source(source)
      , _progress(progress)
   {
   }
   
protected:
   // Performs the work of the agent.
   void run()
   {
      // Read the source string from the buffer and print a message.
      wstringstream ss;
      ss << L"Computing all permutations of '" << receive(_source) << L"'..." << endl;
      wcout << ss.str();
    
      // Print each progress message.
      unsigned int previous_progress = 0u;
      while (true)
      {         
         unsigned int progress = receive(_progress);

         if (progress > previous_progress || progress == 0u)
         { 
            wstringstream ss;
            ss << L'\r' << progress << L"% complete...";
            wcout << ss.str();
            previous_progress = progress;
         }

         if (progress == 100)
            break;
      }
      wcout << endl;

      // Set the status of the agent to agent_done.
      done();
   }

private:
   // The buffer that contains the source string to permute.
   ISource<wstring>& _source;

   // The buffer that contains progress status.
   ISource<unsigned int>& _progress;
};

// Computes all permutations of the given string. 
void permute_string(const wstring& source,
   Scheduler& permutor_scheduler, Scheduler& printer_scheduler)
{  
   // Message buffer that contains the source string.
   // The permutor and printer agents both read from this buffer.
   single_assignment<wstring> source_string;

   // Message buffer that contains the progress status.
   // The permutor agent writes to this buffer and the printer agent reads
   // from this buffer.
   unbounded_buffer<unsigned int> progress;

   // Create the agents with the appropriate schedulers.
   permutor agent1(source_string, progress, permutor_scheduler);
   printer agent2(source_string, progress, printer_scheduler);

   // Start the agents.
   agent1.start();
   agent2.start();
   
   // Write the source string to the message buffer. This will unblock the agents.
   send(source_string, source);

   // Wait for both agents to finish.
   agent::wait(&agent1);
   agent::wait(&agent2);
}

int wmain()
{
   const wstring source(L"Grapefruit");

   // Compute all permutations on the default scheduler.

   Scheduler* default_scheduler = CurrentScheduler::Get();
  
   wcout << L"With default scheduler: " << endl;
   permute_string(source, *default_scheduler, *default_scheduler);
   wcout << endl;

   // Compute all permutations again. This time, provide a scheduler that
   // has higher context priority to the printer agent.

   SchedulerPolicy printer_policy(1, ContextPriority, THREAD_PRIORITY_HIGHEST);
   Scheduler* printer_scheduler = Scheduler::Create(printer_policy);

   // Register to be notified when the scheduler shuts down.
   HANDLE hShutdownEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
   printer_scheduler->RegisterShutdownEvent(hShutdownEvent);

   wcout << L"With higher context priority: " << endl;
   permute_string(source, *default_scheduler, *printer_scheduler);
   wcout << endl; 

   // Release the printer scheduler.
   printer_scheduler->Release();

   // Wait for the scheduler to shut down and destroy itself.
   WaitForSingleObject(hShutdownEvent, INFINITE);

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

本示例生成以下输出。

With default scheduler:
Computing all permutations of 'Grapefruit'...
100% complete...

With higher context priority:
Computing all permutations of 'Grapefruit'...
100% complete...

尽管这两组任务产生的结果相同，但使用自定义策略的版本使 printer 对象能够以提升的优先级运行，以便其行为响应更快。

编译代码

复制示例代码，并将它粘贴到 Visual Studio 项目中，或粘贴到名为 permute-strings.cpp 的文件中，再在 Visual Studio 命令提示符窗口中运行以下命令。

cl.exe /EHsc permute-strings.cpp

另请参阅

计划程序策略
 异步代理

如何：创建使用特定计划程序策略的代理

示例

编译代码

另请参阅

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