Thread already joined at **

最新推荐文章于 2024-08-02 08:42:17 发布

转载最新推荐文章于 2024-08-02 08:42:17 发布 · 197 阅读

本文介绍了一个Perl脚本中关于线程管理和同步的问题案例。通过控制并发线程的数量，并确保线程安全地进行创建和结束，文章详细分析了线程ID的正确使用方式以及如何避免重复join同一线程的问题。

use strict;
use threads;
use threads::shared;
my $MAXTHREAEDNUM = 20;
my $CURTHREADNUM :shared = 0;

my @threads;

sub startThread
{
## 当前新建的线程数加一：
{
lock($CURTHREADNUM);
$CURTHREADNUM++;
}

print"here is the $CURTHREADNUM thread!n";
sleep(3);

## 当前活动的线程数减一：
{
lock($CURTHREADNUM);
$CURTHREADNUM--;
}
}

[@more@]sub main
{
my $threadid;#壹
for(my $i=0;$i<5;$i++)
{
while(1)
{
if ( $CURTHREADNUM < $MAXTHREAEDNUM)
{
$threadid = threads->create('startThread');
# my $threadid = threads->create('startThread'); #贰
if ( $threadid < 0 )
{
print "To Create Thread Error,Please sleep 30's,Try Again n";
}
push(@threads, $threadid);
last;
}
else
{
print "The max thread num limit, waiting 1 second,Try Again. n" ;
sleep(1);
}
}
}

my $i=0;
foreach my $thread (@threads)
{
$i++;
print "Begin to join $i: ".$thread."n";
$$thread->join();
}

}

######################################################################
# program section
open(STDERR, ">&STDOUT");
print "进程号PID：$$ n";
exit(main());

定义壹运行日志如下：
---------------------------------------------
进程号PID：1660
Begin to join 1: REF(0x18a66a0)
here is the 1 thread!
here is the 2 thread!
here is the 3 thread!
here is the 4 thread!
here is the 5 thread!
Begin to join 2: REF(0x18a66a0)
Thread already joined at thread_test.pl line 58.
-------------------------------------------------------
可以看出 join 1和join 2的$thread值是一样的，即REF(0x18a66a0)，也就是说REF(0x18a66a0)线程在1处做了join后，2处试图再做一次。
Thread already joined at thread_test.pl line 58.错误就可以理解了。

为什么数组@threads中的值是唯一的呢？（把上述脚本 $$thread->join();去掉，可以看出@threads中各元素值均相同）
在线程创建后，即 $threadid = threads->create('startThread');返回的为1对象，定义外部变量时，只会改变变量值，不会改变其地址，
所以printer $threadid 将会为一常量值（第一个返回对象的地址），如下示：
----------------------------------------------------
进程号PID：3288
The created theadid:REF(0x18a66b8)
The created theadid:REF(0x18a66b8)
here is the 1 thread!
here is the 2 thread!
The created theadid:REF(0x18a66b8)
The created theadid:REF(0x18a66b8)
here is the 3 thread!
here is the 4 thread!
here is the 5 thread!
The created theadid:REF(0x18a66b8)
---------------------------------------------------
但printer $threadid会有变化，如下示：
----------------------------------------------------
The created theadid:threads=SCALAR(0x18a7024)
The created theadid:threads=SCALAR(0x18a703c)
here is the 1 thread!
here is the 2 thread!
The created theadid:threads=SCALAR(0x18a7054)
The created theadid:threads=SCALAR(0x18a706c)
here is the 3 thread!
here is the 4 thread!
here is the 5 thread!
The created theadid:threads=SCALAR(0x1a9bc78)
----------------------------------------------------

push(@threads, $threadid);
$threadid为threads->create('startThread');的返回对象，将对象加入数组需要加上"",即为$threadid；
上述语句若改成push(@threads, $threadid);join将会报错：Can't call method "join" without a package or object reference at ...

若将定义改为贰：
运行正常，结果日志如下：
------------------------------------------------------------
进程号PID：2988
here is the 1 thread!
Begin to join 1: REF(0x18a66b8)
here is the 2 thread!
here is the 3 thread!
here is the 4 thread!
here is the 5 thread!
Begin to join 2: REF(0x275e24)
Begin to join 3: REF(0x18a6b8c)
Begin to join 4: REF(0x18a6bb0)
Begin to join 5: REF(0x18a6bd4)
-----------------------------------------------------------

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