标签：style blog color os ar for 文件 div sp
$begin = time(); for ($i=0; $i<10000; $i++) { $fp = fopen("tmp", ‘r+‘); fseek($fp, 0, SEEK_END); fwrite($fp, str_repeat($argv[1],1024*32).PHP_EOL); fclose($fp); } $end = time(); echo "time use: ".($end-$begin).PHP_EOL;
php write.php b
php write.php a
wc -l tmp
10450 tmp
与预期的2W行不相符
seek定位到文件末尾的之后，可能因为其他进程已经写入文件，当前进程进行了覆盖
$begin = time(); for ($i=0; $i<10000; $i++) { $fp = fopen("tmp", ‘a+‘); fwrite($fp, str_repeat($argv[1],1024*32).PHP_EOL); fclose($fp); } $end = time(); echo "time use: ".($end-$begin).PHP_EOL;
php write.php b
php write.php a
wc -l tmp
20000 tmp
与预期的2W行相符，但是检查文件内容
检查脚本，检查一行是不是同时含有a和b
<?php $fp = fopen("tmp", ‘r+‘); while (!feof($fp)) { $line = fgets($fp, 1024*1024); if (strstr($line, ‘a‘) && strstr($line, ‘b‘)) { echo ‘not pass‘.PHP_EOL; for ($i=0;$i<strlen($line);$i++){ echo ord($line[$i]).PHP_EOL; } die; } } echo ‘pass‘.PHP_EOL;
php check.php >ts
ts内容
not pass
97
97
.
.
.
98
98
10
php的fwrite是带buffer的，写入一行的内容大于buffer的长度，进程A和进程B是轮流调用write到同一行，就导致了这种结果
顺序写
$begin = time(); $fp = fopen("tmp", ‘w+‘); for ($i=0; $i<200000; $i++) { fwrite($fp, str_repeat($argv[1],1024*32).PHP_EOL); } fclose($fp); $end = time(); echo "time use: ".($end-$begin).PHP_EOL;
php write.php a
time use: 13
$begin = time(); for ($i=0; $i<200000; $i++) { $fp = fopen("tmp", ‘a+‘); fwrite($fp, str_repeat($argv[1],1024*32).PHP_EOL); fclose($fp); } $end = time(); echo "time use: ".($end-$begin).PHP_EOL;
php write.php a
time use: 16
标签：style blog color os ar for 文件 div sp
原文地址：http://www.cnblogs.com/23lalala/p/3930145.html
