Re: Get PID of child threads

Both top and htop will toggle the display of PID/TID when you press 'H'. The header, somewhat confusingly, remains "PID". In reality, the PID is shared between threads. The ps utility has a separate field for thread ID, called "LWP". In any case, this ID is accessible for the thread via gettid, a Linux-specific syscall...

Here's a snippet that appears to work on my system:

use threads;

sub gettid {
    use Config;
    die if $Config{archname} !~ /x86_64-linux/;

    syscall 186
}

sub diag {
    print "pid=$$ tid=@{[threads->tid]} gettid=@{[gettid]}\n";
}

async { diag }->join for 1..5;
[download]

Edit. s/detach/join/, just in case.

Comment on Re: Get PID of child threads Download Code

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Re^2: Get PID of child threads by TS90 (Novice) on Apr 03, 2017 at 22:29 UTC
Thanks, that works! The syscall for my OS (arm-linux-gnueabihf-thread-multi-64int) is 224. The following works. `use threads; sub gettid { syscall 224 } sub diag { print "pid=$$ tid=@{[threads->tid]} gettid=@{[gettid]}\n"; } async { diag }->detach for 1..5;` [download] pid=16490 tid=1 gettid=16493 pid=16490 tid=2 gettid=16494 pid=16490 tid=3 gettid=16495 pid=16490 tid=4 gettid=16496	[reply] [d/l]

Replies are listed 'Best First'.

Re^2: Get PID of child threads
by TS90 (Novice) on Apr 03, 2017 at 22:29 UTC

use threads;

sub gettid
{
    syscall 224
}

sub diag
{
    print "pid=$$ tid=@{[threads->tid]} gettid=@{[gettid]}\n";
}

async { diag }->detach for 1..5;
[download]

pid=16490 tid=1 gettid=16493
pid=16490 tid=2 gettid=16494
pid=16490 tid=3 gettid=16495
pid=16490 tid=4 gettid=16496

[reply]
[d/l]