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path: root/src/thread/__timedwait.c
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2017-07-04unify the use of FUTEX_PRIVATEJens Gustedt1-1/+1
The flag 1<<7 is used in several places for different purposes that are not always easy to distinguish. Mark those usages that correspond to the flag that is used by the kernel for futexes.
2015-03-02factor cancellation cleanup push/pop out of futex __timedwait functionRich Felker1-9/+13
previously, the __timedwait function was optionally a cancellation point depending on whether it was passed a pointer to a cleaup function and context to register. as of now, only one caller actually used such a cleanup function (and it may face removal soon); most callers either passed a null pointer to disable cancellation or a dummy cleanup function. now, __timedwait is never a cancellation point, and __timedwait_cp is the cancellable version. this makes the intent of the calling code more obvious and avoids ugly dummy functions and long argument lists.
2015-02-27fix failure of internal futex __timedwait to report ECANCELEDRich Felker1-1/+1
as part of abstracting the futex wait, this function suppresses all futex error values which callers should not see using a whitelist approach. when the masked cancellation mode was added, the new ECANCELED error was not whitelisted. this omission caused the new pthread_cond_wait code using masked cancellation to exhibit a spurious wake (rather than acting on cancellation) when the request arrived after blocking on the cond var.
2014-09-06use weak symbols for the POSIX functions that will be used by C threadsJens Gustedt1-3/+6
The intent of this is to avoid name space pollution of the C threads implementation. This has two sides to it. First we have to provide symbols that wouldn't pollute the name space for the C threads implementation. Second we have to clean up some internal uses of POSIX functions such that they don't implicitly drag in such symbols.
2014-08-22fix fallback checks for kernels without private futex supportRich Felker1-1/+1
for unknown syscall commands, the kernel produces ENOSYS, not EINVAL.
2014-08-15make futex operations use private-futex mode when possibleRich Felker1-15/+9
private-futex uses the virtual address of the futex int directly as the hash key rather than requiring the kernel to resolve the address to an underlying backing for the mapping in which it lies. for certain usage patterns it improves performance significantly. in many places, the code using futex __wake and __wait operations was already passing a correct fixed zero or nonzero flag for the priv argument, so no change was needed at the site of the call, only in the __wake and __wait functions themselves. in other places, especially where the process-shared attribute for a synchronization object was not previously tracked, additional new code is needed. for mutexes, the only place to store the flag is in the type field, so additional bit masking logic is needed for accessing the type. for non-process-shared condition variable broadcasts, the futex requeue operation is unable to requeue from a private futex to a process-shared one in the mutex structure, so requeue is simply disabled in this case by waking all waiters. for robust mutexes, the kernel always performs a non-private wake when the owner dies. in order not to introduce a behavioral regression in non-process-shared robust mutexes (when the owning thread dies), they are simply forced to be treated as process-shared for now, giving correct behavior at the expense of performance. this can be fixed by adding explicit code to pthread_exit to do the right thing for non-shared robust mutexes in userspace rather than relying on the kernel to do it, and will be fixed in this way later. since not all supported kernels have private futex support, the new code detects EINVAL from the futex syscall and falls back to making the call without the private flag. no attempt to cache the result is made; caching it and using the cached value efficiently is somewhat difficult, and not worth the complexity when the benefits would be seen only on ancient kernels which have numerous other limitations and bugs anyway.
2011-08-07simplify unified timed wait code, drop support for newer methodRich Felker1-31/+28
the new absolute-time-based wait kernelside was hard to get right and basically just code duplication. it could only improve "performance" when waiting, and even then, the improvement was just slight drop in cpu usage during a wait. actually, with vdso clock_gettime, the "old" way will be even faster than the "new" way if the time has already expired, since it will not invoke any syscalls. it can determine entirely in userspace that it needs to return ETIMEDOUT.
2011-08-03timedwait: play it safe for nowRich Felker1-1/+1
it's unclear whether EINVAL or ENOSYS is used when the operation is not supported, so check for both...
2011-08-02correctly handle old kernels without FUTEX_WAIT_BITSETRich Felker1-1/+1
futex returns EINVAL, not ENOSYS, when op is not supported. unfortunately this looks just like EINVAL from other causes, and we end up running the fallback code and getting EINVAL again. fortunately this case should be rare since correct code should not generate EINVAL anyway.
2011-08-02unify and overhaul timed futex waitsRich Felker1-14/+39
new features: - FUTEX_WAIT_BITSET op will be used for timed waits if available. this saves a call to clock_gettime. - error checking for the timespec struct is now inside __timedwait so it doesn't need to be duplicated everywhere. cond_timedwait still needs to duplicate it to avoid unlocking the mutex, though. - pushing and popping the cancellation handler is delegated to __timedwait, and cancellable/non-cancellable waits are unified.
2011-04-17overhaul pthread cancellationRich Felker1-1/+1
this patch improves the correctness, simplicity, and size of cancellation-related code. modulo any small errors, it should now be completely conformant, safe, and resource-leak free. the notion of entering and exiting cancellation-point context has been completely eliminated and replaced with alternative syscall assembly code for cancellable syscalls. the assembly is responsible for setting up execution context information (stack pointer and address of the syscall instruction) which the cancellation signal handler can use to determine whether the interrupted code was in a cancellable state. these changes eliminate race conditions in the previous generation of cancellation handling code (whereby a cancellation request received just prior to the syscall would not be processed, leaving the syscall to block, potentially indefinitely), and remedy an issue where non-cancellable syscalls made from signal handlers became cancellable if the signal handler interrupted a cancellation point. x86_64 asm is untested and may need a second try to get it right.
2011-04-06consistency: change all remaining syscalls to use SYS_ rather than __NR_ prefixRich Felker1-1/+1
2011-04-06major semaphore improvements (performance and correctness)Rich Felker1-1/+1
1. make sem_[timed]wait interruptible by signals, per POSIX 2. keep a waiter count in order to avoid unnecessary futex wake syscalls
2011-03-19if returning errno value directly from a syscall, we need to negate it.Rich Felker1-1/+1
2011-03-19syscall overhaul part two - unify public and internal syscall interfaceRich Felker1-2/+1
with this patch, the syscallN() functions are no longer needed; a variadic syscall() macro allows syscalls with anywhere from 0 to 6 arguments to be made with a single macro name. also, manually casting each non-integer argument with (long) is no longer necessary; the casts are hidden in the macros. some source files which depended on being able to define the old macro SYSCALL_RETURNS_ERRNO have been modified to directly use __syscall() instead of syscall(). references to SYSCALL_SIGSET_SIZE and SYSCALL_LL have also been changed. x86_64 has not been tested, and may need a follow-up commit to fix any minor bugs/oversights.
2011-03-16don't expose EAGAIN, etc. from timed futex wait to callerRich Felker1-1/+4
2011-02-12initial check-in, version 0.5.0v0.5.0Rich Felker1-0/+21