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3. shmctl

shmctl

描述 (Description)

此函数使用带有ARG的CMD控制ID引用的共享内存段。 您需要导入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 (Syntax)

以下是此函数的简单语法 -

shmctl ID, CMD, ARG

返回值 (Return Value)

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

例子 (Example)

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，该程序检索与$ 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，然后在reader.pl中运行，然后它将产生以下结果。

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