我编写了一个小测试程序以弄清楚如何与人交谈poll。我创建了三个文件testa，testb，testc和写入字符串hello\n到第一。因此，这是我的调用poll：

poll(polls.data(),polls.size(),-1)

根据联机帮助页，超时-1应指示syscall永不超时。但是，它不断返回而没有任何内容可供读取。我总是消耗输入的一个字节，并且可以看到hello\n正在打印的内容，但是民意调查并没有就此停止。它只是假装有一些东西要读。

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/fcntl.h>
#include <sys/poll.h>
#include <unistd.h>
#include <errno.h>

#include <vector>
#include <map>
#include <string>
#include <iostream>

typedef int fd_t;

int main() {
  fd_t const a = open("testa",O_RDONLY);
  fd_t const b = open("testb",O_WRONLY);
  fd_t const c = open("testc",O_RDWR);
  std::map<fd_t,std::string> names{{{a,"testa"},{b,"testb"},{c,"testc"}}};

  std::vector<pollfd> polls;
  polls.push_back(pollfd{a, POLLIN, 0});
  polls.push_back(pollfd{b, 0, 0});
  polls.push_back(pollfd{c, POLLIN, 0});

  while (poll(polls.data(),polls.size(),-1)) {
    for (auto p : polls) {
      if ((p.revents & (POLLIN|POLLERR)) == POLLIN) {
        std::cout << "{" << p.fd << ", " << p.events << ", " << p.revents << "} ";
        char byte;
        auto const rr = read(p.fd,&byte,1);
        auto const en = errno;
        if (rr) {
          std::cout << "File " << names[p.fd] << " says something: '" << ((int)byte) << " (" << (((' '<byte) && (byte<127))?byte:'\0') << ")" << "' \n";
        } else {
          std::cout << "Strange (file " << names[p.fd] << "). errno says " << en << "\n";
        }
      }
    }
  }
}

我得到的是：

{3, 1, 1} File testa says something: '104 (h)' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} File testa says something: '101 (e)' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} File testa says something: '108 (l)' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} File testa says something: '108 (l)' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} File testa says something: '111 (o)' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} File testa says something: '10 ()' 
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} Strange (file testa). errno says 0
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} Strange (file testa). errno says 0
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} Strange (file testa). errno says 0
{5, 1, 1} Strange (file testc). errno says 0
{3, 1, 1} Strange (file testa). errno says 0
{5, 1, 1} Strange (file testc). errno says 0

（永远重复最后两行）

我g++ -Wall -Wextra -std=c++11 poll.cpp -o poll在3.10-2-amd64内核上构建。