Re: [PATCH] pthread_once hangs when init routine throws an exception [BZ #18435]

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

On 09/06/15 20:43, Martin Sebor wrote:
> Attached is an updated version of the patch that addresses
> the LDFLAGS -> LDLIBS comment. Retested on ppc64.
> 
> Is it okay to commit?
> 
> Martin
> 
> On 05/31/2015 03:37 PM, Martin Sebor wrote:
>> > The C++ 2011 std::call_once function is specified to allow
>> > the initialization routine to exit by throwing an exception.
>> > Such an execution, termed exceptional, requires call_once to
>> > propagate the exception to its caller. A program may contain
>> > any number of exceptional executions but only one returning
>> > execution (which, if it exists, must be the last execution
>> > with the same once flag).
>> >
>> > On POSIX systems such as Linux std::call_once is implemented
>> > in terms of pthread_once. However, as discussed in libstdc++
>> > bug 66146 - "call_once not C++11-compliant on ppc64le," GLIBC's
>> > pthread_once hangs when the initialization function exits by
>> > throwing an exception on at least arm and ppc64 (though
>> > apparently not on x86_64). This effectively prevents call_once
>> > from conforming to the C++ requirements since there doesn't
>> > appear to be a thread-safe way to work around this problem in
>> > libstdc++.
>> >
>> > The attached patch changes pthread_once to handle gracefully
>> > init functions that exit by throwing exceptions. It has been
>> > tested on ppc64, ppc64le, and x86_64 with no regressions.
...
> diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
> index 84a7105..72d3e23 100644
> --- a/nptl/pthreadP.h
> +++ b/nptl/pthreadP.h
> @@ -536,16 +536,9 @@ extern void __librt_disable_asynccancel (int oldtype)
>  extern void __pthread_cleanup_push (struct _pthread_cleanup_buffer *buffer,
>  				    void (*routine) (void *), void *arg)
>       attribute_hidden;
> -# undef pthread_cleanup_push
> -# define pthread_cleanup_push(routine,arg) \
> -  { struct _pthread_cleanup_buffer _buffer;				      \
> -    __pthread_cleanup_push (&_buffer, (routine), (arg));
>  
>  extern void __pthread_cleanup_pop (struct _pthread_cleanup_buffer *buffer,
>  				   int execute) attribute_hidden;
> -# undef pthread_cleanup_pop
> -# define pthread_cleanup_pop(execute) \
> -    __pthread_cleanup_pop (&_buffer, (execute)); }
>  #endif
>  
>  extern void __pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,

this broke

nptl/tst-join5
nptl/tst-once3

tests on aarch64.

the cleanup handler of the pthread_once and pthread_join
implementation don't run when they are canceled.