semctl
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小牛编辑
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2023-12-01
描述 (Description)
此函数控制System V信号量。 您需要导入IPC:SysV模块以获取CMD的正确定义。 该函数调用系统semctl()函数。
语法 (Syntax)
以下是此函数的简单语法 -
semctl ID, SEMNUM, CMD, ARG
返回值 (Return Value)
此函数在失败时返回undef,0但在成功时返回true。
例子 (Example)
以下示例代码显示其基本用法,创建信号量并增加其值 -
#!/usr/bin/perl -w
# Assume this file name is 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&在后台运行上面的程序,然后写下另一个程序。 这里Left将信号量设置为2并且Right将Right设置为Right并将信号量重置为0.这将一直持续到Left完成其循环,然后使用semctl()销毁信号量
#!/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 $! ";
}
执行上述代码时,会产生以下结果 -
Right....
Left....
Right....
Left....
Right....
Left....
Right....
Left....
Right....
Left....