Perl shmctl 函数

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  描述

  shmctl 使用带有ARG的CMD控制ID引用的共享内存段。您将需要导入IPC::SysV模块以获取下表中定义的命令令牌。

  
  Command  Description
  IPC_STAT    Places the current value of each member of
     the data structure associated with ID into
     the scalar ARG
  
  IPC_SET  Sets the value of the following members o
     of the data structure associated with ID to
     the corresponding values found in the packed
     scalar ARG
  
  IPC_RMID    Removes the shared memory identifier specified
     by ID from the system and destroys the shared
     memory segment and data structure associated
     with it
  
  SHM_LOCK    Locks the shared memory segment specified by ID
     in memory
  
  SHM_UNLOCK  Unlocks the shared memory segment specified by ID
  

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  句法

  以下是此函数的简单语法-

  
  shmctl ID, CMD, ARG
  

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  返回值

  该函数在失败时返回undef，返回0，但如果shmctl（）的返回值为0，则返回true。
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  示例

  以下是显示其基本用法的示例代码-

   
  # Assume this file name is  writer.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_RMID {0}'        unless defined &IPC_RMID;
  
  $key  = 12345;
  $size = 80;
  $message = "Pennyfarthingale.";
  
  # Create the shared memory segment
  
  $key = shmget($key, $size, &IPC_CREAT | 0777 ) or die "Can't shmget: $!";
  
  # Place a string in itl
  shmwrite( $id, $message, 0, 80 ) or die "Can't shmwrite: $!";
  
  
  sleep 20;
  
  # Delete it;
  
  shmctl( $id, &OPC_RMID, 0 ) or die "Can't shmctl: $! ";
  

  编写一个读取程序，该程序检索与$ key相对应的内存段，并使用shmread（）;读取其内容。

   
  # Assume this file name is reader.pl
  
  $key = 12345;
  $size = 80;
  
  # Identify the shared memory segment
  $id = shmget( $key, $size, 0777 ) or die "Can't shmget: $!";
  
  # Read its contents itno a string
  shmread($id, $var, 0, $size) or die "Can't shmread: $!";
  
  print $var;
  

  现在，首先在后台运行writer.pl程序，然后在reader.pl中运行，它将产生以下结果。

  
  $perl writer.pl&
  $perl reader.pl
  
  Pennyfrathingale