前段时间某个需求：客户提交简单的表单可以创建一个适应于全终端（pc，pad，phone）的刮刮卡活动h5页面，其中涉及到客户可在线生成限额6w奖品码的功能。
因为需要保持每个活动奖品码的唯一，我们先是准备用php的uniqid函数来生成uuid（universally unique identifier，也叫guid，为全局唯一标识符，是一种由算法生成的唯一标识）来生成。
但当我们用生成1w测试时候，发现生成过些需要几十秒，还不包括插入至数据库的时间，然后用xhprof写了个简单例子进行性能测试
<?php
xhprof_enable(xhprof_flags_cpu|xhprof_flags_memory);
function myfunc(){
for($i=0;$i<10000;$i++){
$data = uniqid();
}
}
myfunc();
$data = xhprof_disable();
print_r($data);
测试结果：
[myfunc==>uniqid] => array(
[ct] => 10000
[wt] => 39975062
[cpu] => 0
[mu] => 960752
[pmu] => 0
)
竟然需要接近40秒的时间生成，单次执行需要3969微秒，也即是0.003969秒生成。如果用户提交表单的同时生成兑换码，最坏情况下需要4分钟才给用户反应，当然可以用消息队列异步生成，但是为啥uniqid需要如此多的时间来生成一个简单的字符串呢？
然后去查看uniqid的实现源码，代码贴在下面
php_function(uniqid)
{
char *prefix = "";
#if defined(__cygwin__)
zend_bool more_entropy = 1;
#else
zend_bool more_entropy = 0;
#endif
char *uniqid;
int sec, usec, prefix_len = 0;
struct timeval tv;
if (zend_parse_parameters(zend_num_args() tsrmls_cc, "|sb", &prefix, &prefix_len,
&more_entropy)) {
return;
}
#if have_usleep && !defined(php_win32)
if (!more_entropy) {
#if defined(__cygwin__)
php_error_docref(null tsrmls_cc, e_warning, "you must use 'more entropy' under cygwin");
return_false;
#else
usleep(1);
#endif
}
#endif
gettimeofday((struct timeval *) &tv, (struct timezone *) null);
sec = (int) tv.tv_sec;
usec = (int) (tv.tv_usec % 0x100000);
/* the max value usec can have is 0xf423f, so we use only five hex
* digits for usecs.
*/
if (more_entropy) {
spprintf(&uniqid, 0, "%s%08x%05x%.8f", prefix, sec, usec, php_combined_lcg(tsrmls_c) * 10);
} else {
spprintf(&uniqid, 0, "%s%08x%05x", prefix, sec, usec);
}
return_string(uniqid, 0);
}
看逻辑也没有复杂的操作，也是对现在时间秒和微秒进行简单的处理，然后写了个简单的测试
int getuniqid( char * uid) {
int sec, usec;
struct timeval tv;
gettimeofday(( struct timeval *) &tv, ( struct timezone *) null);
sec = ( int) tv. tv_sec;
usec = ( int ) (tv.tv_usec % 0x100000);
sprintf(uid, "%08x%05x" , sec, usec);
return 1;
}
执行1w次也就需要2000微秒，这又是为啥？但是我们发现生成的uid中存在大量的重复，这是才注意点原代码中的usleep函数，
加上usleep函数在测试，这次和php结果一致也需要将近40秒，usleep在此为了保持每次生成的uid不同。
那问题出现在usleep函数上了，然后在usleep前后加上取间隔时间，代码如下
struct timeval start, end;
gettimeofday(( struct timeval *) &start, ( struct timezone *) null);
usleep(1);
gettimeofday(( struct timeval *) &end, ( struct timezone *) null);
unsigned long space = (end.tv_sec - start. tv_sec) * 1000000 + end.tv_usec
- start. tv_usec;
spacecost += space;
最后发现生成1w奖品码需要39.99587739.995877秒，而usleep间隔时间总和39.982442m，通过打印usleep时间发现每次usleep(1)从进程挂起到唤醒需要4000微秒,本来就知道usleep达不到精度，也也相差太远了点。
最后用了下面代码生成奖品码
/**
* 生成兑换码并保存到数据库 返回setno
* $pageid 活动id
* $level 奖品等级
* $numbers 生成奖品的个数
*/
public static function generatecdkeyandsave($pageid,$level,$numbers){
$level1prefix =array(2,5,9,'e','f','m','n','q','k','z');//一等奖的前缀
$level2prefix =array(1,3,7,'a','c','j','r','u','v','x');//二等奖的前置
$level3prefix = array(4,6,8,'b','d','g','h','i','l','o','p','r','s','t','w','y');//三等奖的前缀
if(empty($pageid) || empty($level) || empty($numbers)) return false;
$levelprefix =$level1prefix;
if($level==2) $levelprefix = $level2prefix;
if($level==3) $levelprefix = $level3prefix;
$codes =array();
$now = time();
for($i=0;$i<$numbers;$i++){
$prefixkey = array_rand($levelprefix);
$prefix = self::coupon_prefix.$levelprefix[$prefixkey];
//$code =base_convert(hexdec(md5(uniqid())),10,26); 服务器上面uniqid执行慢的要死
//$code =base_convert(hexdec(md5($pageid.'a#1$v&'.$i)),10,26);//数据过多 hexdec丢失大量精度
$code1 = base_convert(substr(md5($pageid.$i.$now), 0, 10), 16, 36);
$code2 = base_convert($i, 10, 26);
$code2len = strlen($code2);
if ($code2len == 1) {
$code2 .= chr(rand(82, 90)) . chr(rand(82, 90)) . chr(rand(82, 90));
}
else if ($code2len == 2) {
$code2 .= chr(rand(82, 90)) . chr(rand(82, 90));
}
else if ($code2len == 3) {
$code2 .= chr(rand(82, 90));
}
$code =$code1.$code2;
$codes[] = $prefix.strtoupper($code);
}
return $codes;
}
附带uuid测试代码
#include <stdio.h>
#include <malloc.h>
#include <sys/time.h>
#include <unistd.h>
unsigned long sleepcost = 0;
int getuniqid( char * uid,int times) {
struct timeval start, end;
gettimeofday(( struct timeval *) &start, ( struct timezone *) null);
usleep(1);
gettimeofday(( struct timeval *) &end, ( struct timezone *) null);
unsigned long space = (end.tv_sec - start. tv_sec) * 1000000 + end.tv_usec
- start. tv_usec;
sleepcost += space;
if (0 == times%1000) printf ("\n-----sleep cost-------\n%lu usec\n", space);
int sec, usec;
struct timeval tv;
gettimeofday(( struct timeval *) &tv, ( struct timezone *) null);
sec = ( int) tv. tv_sec;
usec = ( int ) (tv.tv_usec % 0x100000);
sprintf(uid, "%08x%05x" , sec, usec);
return 1;
}
int main( int argc, char * argv[]) {
struct timeval start, end;
gettimeofday(( struct timeval *) &start, ( struct timezone *) null);
for ( int i = 1; i <= 10000; i++) {
char data[20];
getuniqid(data,i);
}
gettimeofday(( struct timeval *) &end, ( struct timezone *) null);
unsigned long space = (end.tv_sec - start. tv_sec) * 1000000 + end.tv_usec
- start. tv_usec;
printf( "\n-----cost-------\n% lu usec\n \n-----sum sleep sost-------\n% lu usec\n" , space,sleepcost);
}