Subj : Re: process vs. thread ids on linux
To   : comp.programming.threads
From : David Schwartz
Date : Thu Jun 02 2005 12:25 pm


<jpknott@gmail.com> wrote in message 
news:1117731595.153044.229410@g49g2000cwa.googlegroups.com...

> However, a ps -am gives me this:
>
> 19103 pts/2    00:00:00 ttest
> 19104 pts/2    00:00:00 ttest
> 19105 pts/2    00:00:00 ttest
> 19106 pts/2    00:00:00 ttest
> 19107 pts/2    00:00:00 ttest
> 19108 pts/2    00:00:00 ttest
> 19109 pts/2    00:00:00 ttest
> 19110 pts/2    00:00:00 ttest
> 19111 pts/2    00:00:00 ttest
> 19112 pts/2    00:00:00 ttest
> 19113 pts/2    00:00:00 ttest

    What you are actually seeing on the left is the thread ID, or the KSE 
ID, or whatever you want to call it. It is *NOT* a process ID.

> So, what is going on here?   If the kernel is indeed assigning a new
> pid to each thread, how can I get to that id (since getpid() doesn't
> work).  Why doesn't getpid() work, anyway?    And can I then use these
> pids to send signals directly to a particular thread (which I was under
> the impression was not possible)?

    It is not assigning a new pid to each thread, it is assigning a new tid 
to each thread.

    If you blame the Linux kernel, then the problem is that the Linux kernel 
does not really have a clear notion of a process ID. If you blame ps, then 
the problem is that 'ps' displays the thread ID instead of the process ID, 
or mislabels the column.

    Personally, I blame 'ps'. I believe this is a bug in ps. If it is going 
to label a column "PID", then it should contain the value 'getpid' would 
return, not some other value.

    DS

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