perl semget()函數

perl semget()函數例子，semget()函數實例代碼 - 傳回的信號量ID與KEY

語法

semget KEY, NSEMS, FLAGS

定義和用法

傳回的信號量ID與KEY，使用該係統的函數semget()。即，查找與KEY的信號。

返回值

• undef - 失敗時

• 0，但真正成功

例子

試試下麵的例子：創建一個信號量，它的值增加

#!/usr/bin/perl -w
#by www.gitbook.net
# 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
$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 );

運行上麵的程序中使用$left.pl&運行到後台，並寫另一個程序。在這裡留下設置為2的信號和右鍵打印Right和複位信號為0。 這種情況持續下去，直到左鍵完成其循環後，它破壞了semctl()的信號

#!/usr/bin/perl -w
# by www.gitbook.net
# 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 $! ";
}

現在運行right.pl的，它會產生以下結果：

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