Re: For review: pthread_cancel.3

[Loic Domaigne <tech-Z4JMKDdsf89Wk0Htik3J/w@public.gmane.org>]

Gidday Michael,

>>> Asynchronous cancelability
>>> means that the thread can be canceled at any time
>>> (usually immediately, but the system does not guarantee this).
>>> Deferred cancelability means that cancellation will be delayed until
>>> the thread next calls a function that is a
>>> .IR "cancellation point" .
>>> A list of functions that are or may be cancellation points is 
>>> provided in
>>> .IR pthreads (7).
>>
>> It is very important to document the list of functions that are/are 
>> not CP in the "may be a CP" list: this is system specific and belongs 
>> to the system documentation.
> 
> For man-pages-3.14, I have added POSIX.1's lists of "are" and "may be"
> cancellation points to pthreads.7.
> 
> However, it unclear to me how one determines the list of functions
> that are cancellation points under glibc.  Do you have some ideas
> about this?

I checked out, and I found no obvious to extract the information 
automatically from the source. We may have to ask support from the Glibc 
folks.


>>> .SH NOTES
>>> On Linux, cancellation is implemented using signals.
>>> Under the NPTL threading implementation,
>>> the first real-time signal (i.e., signal 32) is used for this purpose.
>>
>> Hmmm... You are right: NPTL uses the first real-time signal (32) 
>> provided by the *kernel*. As a matter of fact, Glibc reserves kernel 
>> real-time signals 32 and 33 for NPTL; real-time queued signals 
>> available to the application ranges from SIGRTMIN (34) to SIGRTMAX(64).
> 
> Yes... exactly.
> 
>>> On LinuxThreads, the second real-time signal is used,
>>> if real-time signals are available, otherwise
>>> .B SIGUSR2
>>> is used.
>>
>> IIRC, this was true on 'older LinuxThreads'. Never used real-time 
>> queued signals as well ? (To verify...)
> 
> I'm not quite sure what you want to say there.  Can you say some
> more please.

Sorry, typo and missing words make this sentence hard to understand... 
Second try:

Newer version of LinuxThreads uses RT signal as well? (this claim has to 
be verified).

> 
>>> .SH EXAMPLE
> [...]
> 
>> sleep(3) is a CP on Linux (AFAIR, sleep is a "may be CP").
> 
> Not sure what you are wanting to saying here; should something
> be changed in the page?  (BTW: sleep() *is* a CP in POSIX.1.)
> 
> [...]

I hadn't the list at hand, and I thought mistakenly that sleep() is not 
a mandatory CP. Thanks for the note.

Cheers,
Loïc.
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