Perl shmctl 函数
描述
此函数控制 ID 引用的共享内存段,使用 CMD 和 ARG。 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
语法
以下是此函数的简单语法 −
shmctl ID, CMD, ARG
返回值
此函数在失败时返回 undef,如果 shmctl() 的返回值为 0,则返回 0 但为真。
示例
以下是显示其基本用法的示例代码 −
#!/usr/bin/perl # 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,它检索与 $key 对应的内存段并使用 shmread(); 读取其内容。
#!/usr/bin/perl # 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,然后运行 reader.pl,然后它将产生以下结果。
$perl writer.pl& $perl reader.pl Pennyfrathingale