Perl semctl 函数

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  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。
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  句法

  以下是此函数的简单语法-

  
  semctl ID, SEMNUM, CMD, ARG
  

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  返回值

  该函数在失败时返回undef，在成功时返回0，但返回true。
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  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....