[PATCH 18/19] manual: Add pthread_attr_setsigmask_np, pthread_attr_getsigmask_np

Florian Weimer fweimer@redhat.com
Wed Jun 3 09:26:33 GMT 2020


* Michael Kerrisk:

> Hi Florian,
>
> On Tue, May 19, 2020 at 2:04 PM Florian Weimer via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>> And the PTHREAD_ATTR_NO_SIGMASK_NP constant.
>> ---
>>  manual/threads.texi | 47 +++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 47 insertions(+)
>>
>> diff --git a/manual/threads.texi b/manual/threads.texi
>> index a425635179..28d7cf2abd 100644
>> --- a/manual/threads.texi
>> +++ b/manual/threads.texi
>> @@ -625,6 +625,7 @@ the standard.
>>  @menu
>>  * Default Thread Attributes::             Setting default attributes for
>>                                           threads in a process.
>> +* Initial Thread Signal Mask::            Setting the initial mask of threads.
>>  * Waiting with Explicit Clocks::          Functions for waiting with an
>>                                            explicit clock specification.
>>  @end menu
>> @@ -671,6 +672,52 @@ The system does not have sufficient memory.
>>  @end table
>>  @end deftypefun
>>
>> +@node Initial Thread Signal Mask
>> +@subsubsection Controlling the Initial Signal Mask of a New Thread
>> +
>> +@Theglibc{} provides a way to specify the initial signal mask of a
>> +thread created using @code{pthread_create}, passing a thread attribute
>> +object configured for this purpose.
>> +
>> +These functions achieve the same effect as blocking all signals using
>> +@code{pthread_sigmask} before creating the thread, and setting the
>> +desired signal mask from the new thread, but in a more explicit
>> +fashion.
>
> So, I'm not quite clear what's going on here. Is it like this:
>
> First thread
>
> Block all signals
>     |
>     V
> Create new thread --->NEW THREAD ---> Set mask to attr value
>     |
>     V
> Restore signal mask to original value.
>
> If so, maybe that could be explained a bit more explicitly?

I added this as a longer explanation to the end of the section and
dropped the second paragraph quoted above.

>> +@deftypefun int pthread_attr_setsigmask_np (pthread_attr_t *@var{attr}, const sigset_t *@var{sigmask})
>> +@standards{GNU, pthread.h}
>> +@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
>> +Change the initial signal mask specified by @var{attr}.  If
>> +@var{sigmask} is not @code{NULL}, the initial signal mask for new
>> +threads created with @var{attr} is set to @code{*@var{sigmask}}.  If
>> +@var{sigmask} is @code{NULL}, @var{attr} will no longer specify an
>> +explicit signal mask, so that the initial signal mask of the new
>> +thread is inherited from the parent thread creating the new thread.
>
> I don't like "parent" here. Threads are peers.
>
> s/parent thread creating the new thread/creating thread/

This is what I have now:

+@var{sigmask} is @code{NULL}, @var{attr} will no longer specify an
+explicit signal mask, so that the initial signal mask of the new
+thread is inherited from the thread that calls @code{pthread_create}.

>> +
>> +This function returns zero on success, and @code{ENOMEM} on memory
>> +allocation failure.
>> +@end deftypefun
>> +
>> +@deftypefun int pthread_attr_getsigmask_np (const pthread_attr_t *@var{attr}, sigset_t *@var{sigmask})
>> +@standards{GNU, pthread.h}
>> +@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
>> +Retrieve the initial signal mask stored in @var{attr} and write it ot
>
> s/initial// ?
> s/write/save/ ?
> s/ot/to/

Fixed:

+Retrieve the signal mask stored in @var{attr} and copy it to
+@code{*@var{sigmask}}.  If the signal mask has not been set, return

>> +@code{*@var{sigmask}}.  If the signal mask has not been set, return
>> +the special constant @code{PTHREAD_ATTR_NO_SIGMASK_NP}, otherwise
>> +return zero.
>> +
>> +Obtaining the signal mask only works if it has been previously stored
>> +by @code{pthread_attr_setsigmask_np}.  For example, the
>> +@code{pthread_getattr_np} function does not obtain the current signal
>> +mask of the specified thread, and @code{pthread_attr_setsigmask_np}
>> +will subsequently report the signal mask as unset.
>> +@end deftypefun
>
> I see what you're trying to say above, but maybe it would be clearer
> to say something like: all that these APIs are doing is manipulating
> an attribute setting in an object that is used to create new threads
> and pthread_attr_getsigmask_np simply retrieves that attribute setting
> (and never the calling thread's signal mask).

The problem is that this should be really in the documentation of
pthread_getattr_np, which is currently undocumented. 8-(

I'm going to add a comment in front of the paragraph:

+@c Move this to the documentation of pthread_getattr_np once it exists.

I also fixed the second reference to pthread_attr_setsigmask_np (should
have been pthread_attr_getsigmask_np).

We could parse /proc/TID/status in pthread_getattr_np, to obtain the
signal mask of a foreign thread, but that seems over the top to me.

I'm going to post a new patch shortly.

Thanks,
Florian



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