PHP uniqid函數執行緩慢的問題

前段時間某個需求：客戶提交簡單的表單可以創建一個適應於全終端（PC，Pad，Phone）的刮刮卡活動H5頁面，其中涉及到客戶可在線生成限額6W獎品碼的功能。
因為需要保持每個活動獎品碼的唯一，我們先是準備用PHP的uniqid函數來生成UUID（Universally Unique IDentifier，也叫GUID，為全局唯一標識符，是一種由算法生成的唯一標識）來生成。
但當我們用生成1W測試時候，發現生成過些需要幾十秒，還不包括插入至資料庫的時間，然後用xhprof寫了個簡單例子進行性能測試 

<?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);

測試結果：

[myfunc==>uniqid] => Array(
            [ct] => 10000
            [wt] => 39975062
            [cpu] => 0
            [mu] => 960752
            [pmu] => 0
)

竟然需要接近40秒的時間生成，單次執行需要3969微秒，也就是0.003969秒生成。如果用戶提交表單的同時生成兌換碼，最壞情況下需要4分鐘才給用戶反應，當然可以用訊息隊列異步生成，但是為啥uniqid需要如此多的時間來生成一個簡單的字串呢？

接著去查看uniqid的實作原始碼，程式碼貼在下面 

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);
}

看邏輯也沒有複雜的操作，也是對現在時間秒和微秒進行簡單的處理，然後寫了個簡單的測試 

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;
}

執行1W次也就需要2000微秒，這又是為啥？但是我們發現生成的uid中存在大量的重複，這是才注意點原代碼中的usleep函數， 
加上usleep函數在測試，這次和PHP結果一致也需要將近40秒，usleep在此為了保持每次生成的uid不同。
那問題出現在usleep函數上了，然後在usleep前後加上取間隔時間，代碼如下 

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;

最後發現生成1W獎品碼需要39.99587739.995877秒，而usleep間隔時間總和39.982442m，通過打印時間發現通過打印每次usleep(1)從進程掛起到喚醒需要4000微秒,本來就知道usleep達不到精度，也也相差太遠了點。 
最後用了下面程式碼產生獎品碼 

/**
     * 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.&#39;A#1$v&&#39;.$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;
    }

附帶uuid測試程式碼 

#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);
}