perl semctl()函数

转自：http://www.yiibai.com/perl/perl_semctl.html

描述

perl semctl()函数例子，semctl()函数实例代码 - 控制系统V信号量。

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语法

semctl ID, SEMNUM, CMD, ARG

定义和用法

控制系统V信号量。 你将需要进口IPCSysV的模块，以获得正确的定义CMD。 该函数调用系统调用semctl()函数。

返回值

• undef - 失败时

• 0 但真（true)成功时

例子

试试下面的例子：创建一个信号量，增加它的值

#!/usr/bin/perl -w

# Assume this file nam eis left.pl

use IPC::SysV;

#use these next two lines if the previous use fails.
eval 'sub IPC_CREAT {0001000}' unless defined &IPC_CREAT;
eval 'sub IPC_EXCL {0002000}'  unless defined &IPC_EXCL;
eval 'sub IPC_RMID {0}'        unless defined &IPC_RMID;

$key = 1066;

$| = 1;
$num = 0;
$flag = 0;

# Create the semaphor - by www.yiibai.com
$id = semget ( $key, 1, &IPC_EXCL|&IPC_CREAT|0777 ) or 
	die "Can't semget: $!";
foreach( 1..5) {
	$op  = 0;
	$operation = pack( "s*", $num, $op, $flags );
	semop( $id, $operation ) or die "Can't semop: $! ";
	print "Left....\n";
	sleep 1;
	$op = 2;
	$operation = pack( "s*", $num, $op, $flags );
	# add 2 to the semaphore ( now 2 )
	semop( $id, $operation ) or die "Can't semop $! ";
}
semctl (  $id, 0, &IPC_RMID, 0 );

运行上面的程序中使用$left.pl& 背景，并写另一个程序。 在这里留下左键设置为2信号和右键打印右键和复位信号为0。这种情况持续下去，直到左键完成其循环后，它破坏了semctl()信号。

#!/usr/bin/perl -w

# Assume this file name is right.pl

$key = 1066;

$| = 1;
$num = 0;
$flags = 0;

# Identify the semaphore created by left.
$id = semget( $key, 1, 0 ) or die ("Can't semgt : $!" );

foreach( 1..5){
	$op = -1;
	$operation =  pack( "s*", $num, $op, $flags );
	# Add -1 to the semaphore (now 1)
	semop( $id, $operation ) or die " Can't semop $!";
	print "Right....\n";
	sleep 1;
	$operation = pack( "s*", $num, $op, $flags );
	 # Add -1 to the semaphore (now  0)
	semop( $id, $operation ) or die "Can't semop $! ";
}

现在运行right.pl，它会产生以下结果：

Right....
Left....
Right....
Left....
Right....
Left....
Right....
Left....
Right....
Left....