Perl semctl 函数 - 菜鸟教程

描述

semctl 此函数控制System V信号灯。您将需要导入IPC:SysV模块以获取CMD的正确定义。该函数调用系统 semctl（）函数。

句法

以下是此函数的简单语法-


semctl ID, SEMNUM, CMD, ARG

返回值

该函数在失败时返回undef，在成功时返回0，但返回true。

示例

以下是显示其基本用法的示例代码-

 
# 这个文件名为 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 semaphore
$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 );

使用$left.pl ＆在后台运行上述程序，并在另一个程序之后编写。在这里，“左”将信号量设置为2，“右”输出右信号并将信号量重置为0。这一直持续到“左”完成其循环，然后使用semctl（）销毁信号量。

 
# 这个文件名为 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 $! ";
}

执行以上代码后，将产生以下结果--


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