//Introduction to flock function usage on w3school:
PHP flock() function
Definition and Usage
The flock() function locks or releases a file.
If successful, returns true. On failure, returns false.
Grammar
flock(file,lock,block)
Parameter Description
file required. Specifies an open file to be locked or released.
lock required. Specifies which lock type to use.
block is optional. If set to 1 or true, blocks other processes while locking.
Description
The file used by flock() must be an open file pointer.
The lock parameter can be one of the following values:
To obtain a shared lock (reading program), set lock to LOCK_SH (set to 1 in versions prior to PHP 4.0.1).
To obtain an exclusive lock (writing program), set lock to LOCK_EX (set to 2 in versions prior to PHP 4.0.1).
To release a lock (whether shared or exclusive), set lock to LOCK_UN (set to 3 in versions prior to PHP 4.0.1).
If you do not want flock() to block on lock, add LOCK_NB to lock (set to 4 in versions prior to PHP 4.0.1).
Tips and Notes
Tip: The lock operation can be released through fclose(), which will be automatically called when the code is completed.
Note: Since flock() requires a file pointer, you may have to use a special lock file to protect access to files intended to be opened in write mode (adding "w" or "w+" to the fopen() function).
Example
==================================================
From: http://hxsdit.com/1110
PHP comes with a file lock function:
bool flock ( int $handle , int $operation [, int &$wouldblock ] )
$handle is the open file pointer;
$operation can be
"LOCK_SH", shared lock; "LOCK_EX", exclusive lock; "LOCK_UN", releases the lock; "LOCK_NB", prevents blocking when flock is locked.
Here we mainly talk about "LOCK_EX" and "LOCK_NB".
For example, we have two files, as follows.
flocka.php
?View Code PHP
1 2 3 4 5 6 7 8 9 10
$file = 'temp.txt'; $fp = fopen($file,'a'); for($i = 0;$i
flockb.php
?View Code PHP
1 2 3 4 5 6 7 8 9
$file = 'temp.txt'; $fp = fopen($file,'a'); for($i = 0;$i
Run flocka.php first, then flockb.php immediately.
Result:
11111111
22222222
22222222
22222222
22222222
22222222
11111111
11111111
11111111
11111111
Note that when no file lock is added, the two files will write to the txt file at the same time.
Let’s modify the code of the two php files.
flocka.php
?View Code PHP
1 2 3 4 5 6 7 8 9 10 11 12 13
$file = 'temp.txt'; $fp = fopen($file,'a'); if(flock($fp,LOCK_EX)) { for($i = 0;$i
?View Code PHP
1 2 3 4 5 6 7 8 9 10 11 12 13
$file = 'temp.txt'; $fp = fopen($file,'a'); if(flock($fp,LOCK_EX)) { for($i = 0;$i
Also run flocka.php first, and then flockb.php immediately.
You will find that flockb.php is in a waiting state before flocka.php finishes running. Only when flocka.php finishes running, flockb.php will continue to execute.
Output result:
11111111
11111111
11111111
11111111
11111111
22222222
22222222
22222222
22222222
22222222
In addition, when flock is executed, the file lock is automatically released.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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