对于这种情况可以使用多路复用轮询多个IO。
PHP实现并发查询MySQL
PHP的mysqli（mysqlnd驱动）提供多路复用轮询IO（mysqli_poll）和异步查询（MYSQLI_ASYNC、mysqli_reap_async_query），使用这两个特性实现并发查询，示例代码：
<?php
$sqls = array(
'SELECT * FROM `mz_table_1` LIMIT 1000,10',
'SELECT * FROM `mz_table_1` LIMIT 1010,10',
'SELECT * FROM `mz_table_1` LIMIT 1020,10',
'SELECT * FROM `mz_table_1` LIMIT 10000,10',
'SELECT * FROM `mz_table_2` LIMIT 1',
'SELECT * FROM `mz_table_2` LIMIT 5,1'
);
$links = [];
$tvs = microtime();
$tv = explode(' ', $tvs);
$start = $tv[1] * 1000 + (int)($tv[0] * 1000);
// 链接数据库，并发起异步查询
foreach ($sqls as $sql) {
$link = mysqli_connect('127.0.0.1', 'root', 'root', 'dbname', '3306');
$link->query($sql, MYSQLI_ASYNC); // 发起异步查询，立即返回
$links[$link->thread_id] = $link;
}
$llen = count($links);
$process = 0;
do {
$r_array = $e_array = $reject = $links;
// 多路复用轮询IO
if(!($ret = mysqli_poll($r_array, $e_array, $reject, 2))) {
continue;
}
// 读取有结果返回的查询，处理结果
foreach ($r_array as $link) {
if ($result = $link->reap_async_query()) {
print_r($result->fetch_row());
if (is_object($result))
mysqli_free_result($result);
} else {
}
// 操作完后，把当前数据链接从待轮询集合中删除
unset($links[$link->thread_id]);
$link->close();
$process++;
}
foreach ($e_array as $link) {
die;
}
foreach ($reject as $link) {
die;
}
}while($process < $llen);
$tvs = microtime();
$tv = explode(' ', $tvs);
$end = $tv[1] * 1000 + (int)($tv[0] * 1000);
echo $end - $start,PHP_EOL;
mysqli_poll源码：
#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);
}
