Add support for POSIX semaphores

[gswagere]

BPO	525532
Nosy	@mwhudson, @tim-one, @loewis
Files	thread_pthread.h.sem.diff-c: thread_pthread.h with semaphore support

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/loewis'
closed_at = <Date 2002-03-17.09:54:37.000>
created_at = <Date 2002-03-04.14:50:34.000>
labels = ['interpreter-core']
title = 'Add support for POSIX semaphores'
updated_at = <Date 2002-03-17.09:54:37.000>
user = 'https://bugs.python.org/gswagere'

bugs.python.org fields:

activity = <Date 2002-03-17.09:54:37.000>
actor = 'loewis'
assignee = 'loewis'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2002-03-04.14:50:34.000>
creator = 'gsw_agere'
dependencies = []
files = ['4028']
hgrepos = []
issue_num = 525532
keywords = ['patch']
message_count = 5.0
messages = ['39138', '39139', '39140', '39141', '39142']
nosy_count = 4.0
nosy_names = ['mwh', 'tim.peters', 'loewis', 'gsw_agere']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue525532'
versions = ['Python 2.3']

[gswagere]

thread_pthread.h can be modified to use POSIX
semaphores if available. This is more efficient than
emulating them with mutexes and condition variables,
and at least one platform that supports POSIX
semaphores has a race condition in its condition
variable support.

The new file would still be supporting POSIX threads,
although from both <pthread.h> and <semaphore.h>, so
perhaps ought to be renamed if this patch is accepted.

[tim-one]

Logged In: YES
user_id=31435

Can someone on a pthreads platform please continue with
this? I'm +1 on it via eyeballing.

[mwhudson]

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user_id=6656

Does this belong in the 2.2.x group?

[tim-one]

Logged In: YES
user_id=31435

Changed Group to 2.3.

[loewis]

Logged In: YES
user_id=21627

Thanks for the patch; committed as thread_pthread.h 2.39.