Modify the implementation of libc semaphores so that they can be
overridden by the threads library to provide a userland version
of non-pshared semaphores and cancellation points. Also add
a sem_tim

Modify the implementation of libc semaphores so that they can be
overridden by the threads library to provide a userland version
of non-pshared semaphores and cancellation points. Also add
a sem_timedwait().

The libc version of semaphores always uses kernel semaphores
regardless of whether pshared is set or not. When threads are
not present, it is difficult to get sem_wait() or sem_timedwait()
to do the right thing (since pthread_cond_timedwait() and
pthread_cond_wait() are stubs in libc and just return immediately).

show more ...

Backout revision 1.6, because some stub functions not in libc, and
non-threaded won't build. The cancellation point support should be
further discussed.

Enable cancellation point in sem_wait, it is required by POSIX.
For pshared semaphore, this commit still does not enable cancellation
point, I think there should be a pthread_enter_cancellation_point

Enable cancellation point in sem_wait, it is required by POSIX.
For pshared semaphore, this commit still does not enable cancellation
point, I think there should be a pthread_enter_cancellation_point_np
for libc to implement a safe cancellation point.

show more ...

Eliminate 61 warnings emitted at WARNS=2 (leaving 53 to go).
Only warnings that could be fixed without changing the generated object
code and without restructuring the source code have been handled.

Eliminate 61 warnings emitted at WARNS=2 (leaving 53 to go).
Only warnings that could be fixed without changing the generated object
code and without restructuring the source code have been handled.

Reviewed by: /sbin/md5

show more ...

Add the newly created semaphore to the named semaphore list in sem_open()
so that multiple opens of the same semaphore without an intervening
sem_close() return the same object, and so that sem_close

Add the newly created semaphore to the named semaphore list in sem_open()
so that multiple opens of the same semaphore without an intervening
sem_close() return the same object, and so that sem_close() does not
segfault while trying to remove the item from the list.

show more ...

Add restrict type-qualifier to sem_getvalue().

Welcome the sem_ API to libc!

Reapply r201145 to lib/libc/gen/sem.c

Merge from head at r201628.

# This hasn't been tested, and there are at least three bad commits
# that need to be backed out before the branch will be stable again.

forgot to remove SYM_FBP10. ;-)

Remove unused macros.

Use umtx to implement process sharable semaphore, to make this work,
now type sema_t is a structure which can be put in a shared memory area,
and multiple processes can operate it concurrently.
User

Use umtx to implement process sharable semaphore, to make this work,
now type sema_t is a structure which can be put in a shared memory area,
and multiple processes can operate it concurrently.
User can either use mmap(MAP_SHARED) + sem_init(pshared=1) or use sem_open()
to initialize a shared semaphore.
Named semaphore uses file system and is located in /tmp directory, and its
file name is prefixed with 'SEMD', so now it is chroot or jail friendly.
In simplist cases, both for named and un-named semaphore, userland code
does not have to enter kernel to reduce/increase semaphore's count.
The semaphore is designed to be crash-safe, it means even if an application
is crashed in the middle of operating semaphore, the semaphore state is
still safely recovered by later use, there is no waiter counter maintained
by userland code.
The main semaphore code is in libc and libthr only has some necessary stubs,
this makes it possible that a non-threaded application can use semaphore
without linking to thread library.
Old semaphore implementation is kept libc to maintain binary compatibility.
The kernel ksem API is no longer used in the new implemenation.

Discussed on: threads@

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(S)LIST_HEAD_INITIALIZER takes a (S)LIST_HEAD as an argument.
Fix some wrong usages.
Note: this does not affect generated binaries as this argument is not used.

PR: 137213
Submitted by: Eygene Ryab

(S)LIST_HEAD_INITIALIZER takes a (S)LIST_HEAD as an argument.
Fix some wrong usages.
Note: this does not affect generated binaries as this argument is not used.

PR: 137213
Submitted by: Eygene Ryabinkin (initial version)
MFC after: 1 month

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Make __sem_timedwait() consistent with the sem_timedwait() prototype.

Include <sys/types.h> and <limits.h> ourselves, don't assume they are included
through <pthread.h>.

gen/sem.c: Prerequisite for <_semaphore.h>
net/getprotoent.c: USHRT_MAX
net/getservent.c: USHRT_M

Include <sys/types.h> and <limits.h> ourselves, don't assume they are included
through <pthread.h>.

gen/sem.c: Prerequisite for <_semaphore.h>
net/getprotoent.c: USHRT_MAX
net/getservent.c: USHRT_MAX
stdio/ungetwc.c: MB_LEN_MAX
stdio/vfwscanf.c: MB_LEN_MAX

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Prevent memory leak on sem_destroy() by destroying the semaphore's
internal mutex and CV.

Only allow the semaphore to be taken when the value is positive.
Don't decrement it twice when it is taken.

Reported by: kris

Correct check for invalid semaphore on sem_destroy() (s/==/!=/).

Reported by: kris

Correct the weak reference for sem_unlink.

Allow libc's version of sem_trywait() to work for non-pshared mutexes.

Modify the implementation of libc semaphores so that they can be
overridden by the threads library to provide a userland version
of non-pshared semaphores and cancellation points. Also add
a sem_tim

Modify the implementation of libc semaphores so that they can be
overridden by the threads library to provide a userland version
of non-pshared semaphores and cancellation points. Also add
a sem_timedwait().

The libc version of semaphores always uses kernel semaphores
regardless of whether pshared is set or not. When threads are
not present, it is difficult to get sem_wait() or sem_timedwait()
to do the right thing (since pthread_cond_timedwait() and
pthread_cond_wait() are stubs in libc and just return immediately).

show more ...

Backout revision 1.6, because some stub functions not in libc, and
non-threaded won't build. The cancellation point support should be
further discussed.

Enable cancellation point in sem_wait, it is required by POSIX.
For pshared semaphore, this commit still does not enable cancellation
point, I think there should be a pthread_enter_cancellation_point

Enable cancellation point in sem_wait, it is required by POSIX.
For pshared semaphore, this commit still does not enable cancellation
point, I think there should be a pthread_enter_cancellation_point_np
for libc to implement a safe cancellation point.

show more ...

Eliminate 61 warnings emitted at WARNS=2 (leaving 53 to go).
Only warnings that could be fixed without changing the generated object
code and without restructuring the source code have been handled.

Eliminate 61 warnings emitted at WARNS=2 (leaving 53 to go).
Only warnings that could be fixed without changing the generated object
code and without restructuring the source code have been handled.

Reviewed by: /sbin/md5

show more ...

Add the newly created semaphore to the named semaphore list in sem_open()
so that multiple opens of the same semaphore without an intervening
sem_close() return the same object, and so that sem_close

Add the newly created semaphore to the named semaphore list in sem_open()
so that multiple opens of the same semaphore without an intervening
sem_close() return the same object, and so that sem_close() does not
segfault while trying to remove the item from the list.

show more ...