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下图显示了 dataflow_agent 类的完整数据流网络#xff1a; 由于 run 方法是在一个单独的线程上调用的#xff0c;因此在完全连接网络之前#xff0c;其他线程可以将消息发送到网络。 _source 数据成员是一个 unbounded_buffer 对象#xff0c;用于缓冲… 完整的数据流演示
下图显示了 dataflow_agent 类的完整数据流网络 由于 run 方法是在一个单独的线程上调用的因此在完全连接网络之前其他线程可以将消息发送到网络。 _source 数据成员是一个 unbounded_buffer 对象用于缓冲从应用程序发送到代理的所有输入。 为了确保网络能够处理所有输入消息代理会首先链接网络的内部节点然后将该网络的起点 connector 链接到 _source 数据成员。 这可以保证在形成网络的过程中不会处理消息。
由于此示例中的网络是基于数据流而不是基于控制流的网络必须向代理传达它已经完成了对每个输入值的处理并且 Sentinel 节点也已接收到它的值。 此示例使用 countdown_event 对象来指示所有输入值均已经过处理使用 concurrency::event 对象指示 Sentinel 节点已接收到它的值。 countdown_event 类使用 event 对象指示计数器值达到零。 每当数据流网络的头收到一个值时都会递增计数器值。 在处理输入值后网络的每个终端节点都会递减计数器值。 代理形成数据流网络后它会等待 Sentinel 节点设置 event 对象还会等待 countdown_event 对象指示其计数器值已达到零。
下面的示例展示了 control_flow_agent、dataflow_agent 和 countdown_event 类。 wmain 函数创建了 control_flow_agent 和 dataflow_agent 对象并使用 send_values 函数将一系列随机值发送到代理。
// dataflow-agent.cpp
// compile with: /EHsc
#include windows.h
#include agents.h
#include iostream
#include randomusing namespace concurrency;
using namespace std;// A basic agent that uses control-flow to regulate the order of program
// execution. This agent reads numbers from a message buffer and counts the
// number of positive and negative values.
class control_flow_agent : public agent
{
public:explicit control_flow_agent(ISourceint source): _source(source){}// Retrieves the count of negative numbers that the agent received.size_t negatives() {return receive(_negatives);}// Retrieves the count of positive numbers that the agent received.size_t positives(){return receive(_positives);}protected:void run(){// Counts the number of negative and positive values that// the agent receives.size_t negative_count 0;size_t positive_count 0;// Read from the source buffer until we receive// the sentinel value of 0.int value 0; while ((value receive(_source)) ! 0){// Send negative values to the first target and// non-negative values to the second target.if (value 0)negative_count;elsepositive_count;}// Write the counts to the message buffers.send(_negatives, negative_count);send(_positives, positive_count);// Set the agent to the completed state.done();}
private:// Source message buffer to read from.ISourceint _source;// Holds the number of negative and positive numbers that the agent receives.single_assignmentsize_t _negatives;single_assignmentsize_t _positives;
};// A synchronization primitive that is signaled when its
// count reaches zero.
class countdown_event
{
public:countdown_event(unsigned int count 0L): _current(static_castlong(count)) {// Set the event if the initial count is zero.if (_current 0L)_event.set();}// Decrements the event counter.void signal() {if(InterlockedDecrement(_current) 0L) {_event.set();}}// Increments the event counter.void add_count() {if(InterlockedIncrement(_current) 1L) {_event.reset();}}// Blocks the current context until the event is set.void wait() {_event.wait();}private:// The current count.volatile long _current;// The event that is set when the counter reaches zero.event _event;// Disable copy constructor.countdown_event(const countdown_event);// Disable assignment.countdown_event const operator(countdown_event const);
};// A basic agent that resembles control_flow_agent, but uses uses dataflow to
// perform computations when data becomes available.
class dataflow_agent : public agent
{
public:dataflow_agent(ISourceint source): _source(source){}// Retrieves the count of negative numbers that the agent received.size_t negatives() {return receive(_negatives);}// Retrieves the count of positive numbers that the agent received.size_t positives(){return receive(_positives);}protected:void run(){// Counts the number of negative and positive values that// the agent receives.size_t negative_count 0;size_t positive_count 0;// Tracks the count of active operations.countdown_event active;// An event that is set by the sentinel.event received_sentinel;//// Create the members of the dataflow network.//// Increments the active counter.transformerint, int increment_active([active](int value) - int {active.add_count();return value;});// Increments the count of negative values.callint negatives([](int value) {negative_count;// Decrement the active counter.active.signal();},[](int value) - bool {return value 0;});// Increments the count of positive values.callint positives([](int value) {positive_count;// Decrement the active counter.active.signal();},[](int value) - bool {return value 0;});// Receives only the sentinel value of 0.callint sentinel([](int value) { // Decrement the active counter.active.signal();// Set the sentinel event.received_sentinel.set();},[](int value) - bool { return value 0; });// Connects the _source message buffer to the rest of the network.unbounded_bufferint connector;//// Connect the network.//// Connect the internal nodes of the network.connector.link_target(negatives);connector.link_target(positives);connector.link_target(sentinel);increment_active.link_target(connector);// Connect the _source buffer to the internal network to // begin data flow._source.link_target(increment_active);// Wait for the sentinel event and for all operations to finish.received_sentinel.wait();active.wait();// Write the counts to the message buffers.send(_negatives, negative_count);send(_positives, positive_count);// Set the agent to the completed state.done();}private:// Source message buffer to read from.ISourceint _source;// Holds the number of negative and positive numbers that the agent receives.single_assignmentsize_t _negatives;single_assignmentsize_t _positives;
};// Sends a number of random values to the provided message buffer.
void send_values(ITargetint source, int sentinel, size_t count)
{// Send a series of random numbers to the source buffer.mt19937 rnd(42);for (size_t i 0; i count; i){// Generate a random number that is not equal to the sentinel value.int n;while ((n rnd()) sentinel);send(source, n); }// Send the sentinel value.send(source, sentinel);
}int wmain()
{// Signals to the agent that there are no more values to process.const int sentinel 0;// The number of samples to send to each agent.const size_t count 1000000;// The source buffer that the application writes numbers to and // the agents read numbers from.unbounded_bufferint source;//// Use a control-flow agent to process a series of random numbers.//wcout LControl-flow agent: endl;// Create and start the agent.control_flow_agent cf_agent(source);cf_agent.start();// Send values to the agent.send_values(source, sentinel, count);// Wait for the agent to finish.agent::wait(cf_agent);// Print the count of negative and positive numbers.wcout LThere are cf_agent.negatives() L negative numbers. endl;wcout LThere are cf_agent.positives() L positive numbers. endl; //// Perform the same task, but this time with a dataflow agent.//wcout LDataflow agent: endl;// Create and start the agent.dataflow_agent df_agent(source);df_agent.start();// Send values to the agent.send_values(source, sentinel, count);// Wait for the agent to finish.agent::wait(df_agent);// Print the count of negative and positive numbers.wcout LThere are df_agent.negatives() L negative numbers. endl;wcout LThere are df_agent.positives() L positive numbers. endl;
}
输出如下:
Control-flow agent:
There are 500523 negative numbers.
There are 499477 positive numbers.
Dataflow agent:
There are 500523 negative numbers.
There are 499477 positive numbers.
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 dataflow-agent.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 dataflow-agent.cpp
