Perl Parallel :: ForkManager wait_all_children（）需要很长时间

Question

我有一个使用Parallel::ForkManager的脚本。但是，即使在所有子进程完成之后，wait_all_children（）进程也需要很长时间。我知道的方法是打印出一些时间戳（见下文）。有没有人有任何想法可能会导致这种情况（我的机器上有16个CPU核心）？

my $pm = Parallel::ForkManager->new(16); 
for my $i (1..16) { 
    $pm->start($i) and next; 

    ... do something within the child-process ... 

    print (scalar localtime), " Process $i completed.\n"; 
    $pm->finish(); 
} 
print (scalar localtime), " Waiting for some child process to finish.\n"; 
$pm->wait_all_children(); 
print (scalar localtime), " All processes finished.\n"; 

很显然，我会先拿到Waiting for some child process to finish消息，有，比方说，7:08:35时间戳。然后我会得到一个Process i completed消息的列表，最后一个在7:10:30。但是，我没有收到All Processes finished的消息，直到7:16:33（！）。为什么7点到10点和7点16分33秒之间有6分钟的延迟？谢谢！

Answer 1

我尝试这样做：

#!/opt/perl/bin/perl 

use strict; use warnings; 

use Parallel::ForkManager; 

my $pm = Parallel::ForkManager->new(16); 

for my $i (1..16) { 
    $pm->start($i) and next; 
    sleep rand 20; 
    printf "%s : Process %d completed\n", scalar localtime, $i; 
    $pm->finish; 
} 

printf "%s: Waiting for some child to finish\n", scalar localtime; 
$pm->wait_all_children; 

printf "%s: All processes finished.\n", scalar localtime; 

我：

[sinan@archardy Src]$ ./y.pl 
Thu Mar 11 17:14:16 2010 : Process 3 completed 
Thu Mar 11 17:14:16 2010: Waiting for some child to finish 
Thu Mar 11 17:14:18 2010 : Process 8 completed 
Thu Mar 11 17:14:18 2010 : Process 14 completed 
<snip>...</snip> 
Thu Mar 11 17:14:34 2010 : Process 12 completed 
Thu Mar 11 17:14:34 2010: All processes finished.

我perl 5.10.1的Linux上0.7.5Parallel::ForkManager版本。

因此，我的结论是什么问题您有正在发生的事情是会发生什么后果，当你

# ... do something within the child-process ... 

更新：的问题是，你是在finish调用之前打印Process finished message。请尝试以下版本：

#!/opt/perl/bin/perl 

use strict; use warnings; 

use Parallel::ForkManager; 

my $pm = Parallel::ForkManager->new(16); 
$pm->run_on_finish(sub { 
    printf "%s : Process completed: @_\n", scalar localtime 
}); 

for my $i (1..16) { 
    $pm->start($i) and next; 
    sleep rand 20; 
    $pm->finish; 
} 

printf "%s: Waiting for some child to finish\n", scalar localtime; 
$pm->wait_all_children; 

printf "%s: All processes finished.\n", scalar localtime; 

请参阅Callbacks in Parallel::ForkManager documentation了解更多信息。如果延迟消失，那么您观察到的症状是由于您声称分叉过程在完成之前已完成。