[PATCH] Add and use new glibc-internal futex API.

[Torvald Riegel]

This adds new functions for futex operations, starting with wait,
abstimed_wait, reltimed_wait, wake.  They add documentation and error
checking according to the current draft of the Linux kernel futex
manpage.

Waiting with absolute or relative timeouts is split into separate
functions.  This allows for removing a few cases of code duplication in
pthreads code, which uses absolute timeouts; also, it allows us to put
platform-specific code to go from an absolute to a relative timeout into
the platform-specific futex abstractions.  The latter is done by adding
lll_futex_abstimed_wait.  I expect that we will refactor this later on,
depending on how we do the lll_ parts.

Futex operations that can be canceled are also split out into separate
functions suffixed by "_cancelable".

This is a revision of
https://sourceware.org/ml/libc-alpha/2015-01/msg00215.html

I have transformed all the lll_futex_* uses that I'm aware of except the
following:
* Anything related to lowlevellock or mutexes.
* sparc-specific files: I'll send a follow-up patch so this can be
reviewed and tested separately.
* pthread condvar: I'll send a follow-up patch on top of my revised
condvar implementation.
* All tls.h files: Siddhesh wants to look at this area in more detail,
so I'll work with him to see how to best move this to the new API.

Interacting with futex words requires atomic accesses, which isn't done
by most of glibc's current futex callers.  I did not fix these in this
patch to keep the patch easier to review: Using the new futex API is in
most cases a pretty mechanical change, which I didn't want to obfuscate
by lots of other changes to atomics.  The core motivation behind this
patch is to add error handling and improve the internal futex API, not
to change any synchronization.
Nonetheless, using atomics where they are needed is on my list of things
to do, so don't worry :)
Specifically, this is already done in the my new condvar implementation
and in the new semaphore.  It will get done for rwlock in the new
implementation I'm working on.  I also plan to update the barrier
implementation.  For TLS, this is something Siddhesh has on his radar,
AFAIK.  Adhemerval is working on a new cancellation scheme.

I kept the old semaphore code unchanged for now because I don't have a
testing setup for this ready.

Adhemerval, is this API compatible with the new cancellation scheme you
are working on?

Roland, okay for NaCl?

Tested on x86_64-linux.


2015-06-08  Torvald Riegel  <triegel@redhat.com>

	* nptl/futex-internal.h: New file.
	* nptl/allocatestack.c (setxid_mark_thread): Use futex wrappers with
	error checking.
	(setxid_unmark_thread): Likewise.
	(__nptl_setxid): Likewise.
	(__wait_lookup_done): Likewise.
	* nptl/cancellation.c (__pthread_disable_asynccancel): Likewise.
	* nptl/nptl-init.c (sighandler_setxid): Likewise.
	* nptl/pthread_create.c (START_THREAD_DEFN): Likewise.
	* nptl/pthread_once.c (clear_once_control): Likewise.
	(__pthread_once_slow): Likewise.
	* nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow):
	Likewise.
	(__pthread_rwlock_rdlock): Likewise.
	* nptl/pthread_rwlock_timedrdlock.c (pthread_rwlock_timedrdlock):
	Likewise.
	* nptl/pthread_rwlock_timedwrlock.c (pthread_rwlock_timedwrlock):
	Likewise.
	* nptl/pthread_rwlock_tryrdlock.c (__pthread_rwlock_tryrdlock):
	Likewise.
	* nptl/pthread_rwlock_unlock.c (__pthread_rwlock_unlock): Likewise.
	* nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow:
	Likewise.
	* nptl/unregister-atfork.c (__unregister_atfork): Likewise.
	* sysdeps/nacl/exit-thread.h (__exit_thread): Likewise.
	* sysdeps/nptl/aio_misc.h (AIO_MISC_NOTIFY, AIO_MISC_WAIT): Likewise.
	* sysdeps/nptl/fork.c (__libc_fork): Likewise.
	* sysdeps/nptl/gai_misc.h (GAI_MISC_NOTIFY, GAI_MISC_WAIT): Likewise.
	* nptl/pthread_barrier_wait.c (pthread_barrier_wait): Likewise.
	* nptl/pthread_barrier_init.c (pthread_barrier_init): Add comment.
	* nptl/sem_init.c (futex_private_if_supported): Remove.
	* nptl/sem_post.c (futex_wake): Likewise.
	* nptl/sem_waitcommon.c (futex_abstimed_wait, futex_wake): Likewise.
	(do_futex_wait): Use futex wrappers with error checking.
	* nptl/sem_open.c (sem_open): Use FUTEX_SHARED.
	* sysdeps/nptl/lowlevellock-futex.h (lll_futex_abstimed_wait): New.
	* sysdeps/unix/sysv/linux/lowlevellock-futex.h
	(lll_futex_abstimed_wait): New.
	* sysdeps/nacl/lowlevellock-futex.h (lll_futex_abstimed_wait): New.

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