PHP并发查询MySQL的实例代码

#ifndef PHP_WIN32
#define php_select(m, r, w, e, t) select(m, r, w, e, t)
#else
#include "win32/select.h"
#endif
/* {{{ mysqlnd_poll */
PHPAPI enum_func_status
mysqlnd_poll(MYSQLND **r_array, MYSQLND **e_array, MYSQLND ***dont_poll, long sec, long usec, int * desc_num)
{
 struct timeval tv;
 struct timeval *tv_p = NULL;
 fd_set   rfds, wfds, efds;
 php_socket_t max_fd = 0;
 int    retval, sets = 0;
 int    set_count, max_set_count = 0;
 DBG_ENTER("_mysqlnd_poll");
 if (sec < 0 || usec < 0) {
  php_error_docref(NULL, E_WARNING, "Negative values passed for sec and/or usec");
  DBG_RETURN(FAIL);
 }
 FD_ZERO(&rfds);
 FD_ZERO(&wfds);
 FD_ZERO(&efds);
 // 从所有mysqli链接中获取socket链接描述符
 if (r_array != NULL) {
  *dont_poll = mysqlnd_stream_array_check_for_readiness(r_array);
  set_count = mysqlnd_stream_array_to_fd_set(r_array, &rfds, &max_fd);
  if (set_count > max_set_count) {
   max_set_count = set_count;
  }
  sets += set_count;
 }
 // 从所有mysqli链接中获取socket链接描述符
 if (e_array != NULL) {
  set_count = mysqlnd_stream_array_to_fd_set(e_array, &efds, &max_fd);
  if (set_count > max_set_count) {
   max_set_count = set_count;
  }
  sets += set_count;
 }
 if (!sets) {
  php_error_docref(NULL, E_WARNING, *dont_poll ? "All arrays passed are clear":"No stream arrays were passed");
  DBG_ERR_FMT(*dont_poll ? "All arrays passed are clear":"No stream arrays were passed");
  DBG_RETURN(FAIL);
 }
 PHP_SAFE_MAX_FD(max_fd, max_set_count);
 // select轮询阻塞时间
 if (usec > 999999) {
  tv.tv_sec = sec + (usec / 1000000);
  tv.tv_usec = usec % 1000000;
 } else {
  tv.tv_sec = sec;
  tv.tv_usec = usec;
 }
 tv_p = &tv;
 // 轮询，等待多个IO可读，php_select是select的宏定义
 retval = php_select(max_fd + 1, &rfds, &wfds, &efds, tv_p);
 if (retval == -1) {
  php_error_docref(NULL, E_WARNING, "unable to select [%d]: %s (max_fd=%d)",
      errno, strerror(errno), max_fd);
  DBG_RETURN(FAIL);
 }
 if (r_array != NULL) {
  mysqlnd_stream_array_from_fd_set(r_array, &rfds);
 }
 if (e_array != NULL) {
  mysqlnd_stream_array_from_fd_set(e_array, &efds);
 }
 // 返回可操作的IO数量
 *desc_num = retval;
 DBG_RETURN(PASS);
}