Hello Shivansh
On 09/27/2017 01:28 PM, Shivansh Rai wrote:
The following information is not available in the latest version of the
man-page (man-pages-4.13) for getpid(2) (quoting from "kernel/sys.c#L829") -
sys_getpid - return the thread group id of the current process
Note, despite the name, this returns the tgid not the pid. The tgid and
the pid are identical unless CLONE_THREAD was specified on clone() in
which case the tgid is the same in all threads of the same group.
This patch applies against: man-pages-4.13
Relevant commit: 4a22f16636259f503847b0805e04824171b270fc (cc'd Stephen
Rothwell)
@@ -59,6 +59,14 @@
.BR pid_namespaces (7)),
.BR getppid ()
returns 0.
+Despite the name
+.BR getpid ()
+returns the thread group ID of the current process. The TGID and the
+PID are identical unless
+.BR CLONE_THREAD
+was specified on
+.BR clone (2)
+in which case the TGID is same in all threads of the same group.
.\"
.SS C library/kernel differences
From glibc version 2.3.4 up to and including version 2.24,
I'm not sure I understand the intent of your patch. This is how
things are on Linux:
In a multithreaded process (created at the kernel level using
clone(V+CLONE_NEWTHREAD), each thread has a unique (kernel)
thread ID (TID).
All of those threads have the same thread group ID (TGID).
From the user-space perspective, the TGID is the same thing as the PID
(i.e., TID is not the same as PID).
In this sense, the text you propose to add seems rather confusing for
user space. But, maybe I have misunderstood your point. If so, let
me know.
Thanks,
Michael
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