musl/src/stdio/ftrylockfile.c

#include "stdio_impl.h"
#include "pthread_impl.h"
#include <limits.h>

int ftrylockfile(FILE *f)
{
	int tid = __pthread_self()->tid;
	if (f->lock == tid) {
		if (f->lockcount == LONG_MAX)
			return -1;
		f->lockcount++;
		return 0;
	}
	if (f->lock < 0) f->lock = 0;
	if (f->lock || a_cas(&f->lock, 0, tid))
		return -1;
	f->lockcount = 1;
	return 0;
}
implement flockfile api, rework stdio locking 2011-03-12 21:55:45 -05:00			`#include "stdio_impl.h"`
			`#include "pthread_impl.h"`
clean up sloppy nested inclusion from pthread_impl.h this mirrors the stdio_impl.h cleanup. one header which is not strictly needed, errno.h, is left in pthread_impl.h, because since pthread functions return their error codes rather than using errno, nearly every single pthread function needs the errno constants. in a few places, rather than bringing in string.h to use memset, the memset was replaced by direct assignment. this seems to generate much better code anyway, and makes many functions which were previously non-leaf functions into leaf functions (possibly eliminating a great deal of bloat on some platforms where non-leaf functions require ugly prologue and/or epilogue). 2012-11-08 17:04:20 -05:00			`#include <limits.h>`
implement flockfile api, rework stdio locking 2011-03-12 21:55:45 -05:00
			`int ftrylockfile(FILE *f)`
			`{`
replace all remaining internal uses of pthread_self with __pthread_self prior to version 1.1.0, the difference between pthread_self (the public function) and __pthread_self (the internal macro or inline function) was that the former would lazily initialize the thread pointer if it was not already initialized, whereas the latter would crash in this case. since lazy initialization is no longer supported, use of pthread_self no longer makes sense; it simply generates larger, slower code. 2014-06-10 04:02:40 -04:00			`int tid = __pthread_self()->tid;`
simplify and optimize FILE lock handling 2011-03-24 23:16:52 -04:00			`if (f->lock == tid) {`
add proper fuxed-based locking for stdio previously, stdio used spinlocks, which would be unacceptable if we ever add support for thread priorities, and which yielded pathologically bad performance if an application attempted to use flockfile on a key file as a major/primary locking mechanism. i had held off on making this change for fear that it would hurt performance in the non-threaded case, but actually support for recursive locking had already inflicted that cost. by having the internal locking functions store a flag indicating whether they need to perform unlocking, rather than using the actual recursive lock counter, i was able to combine the conditionals at unlock time, eliminating any additional cost, and also avoid a nasty corner case where a huge number of calls to ftrylockfile could cause deadlock later at the point of internal locking. this commit also fixes some issues with usage of pthread_self conflicting with __attribute__((const)) which resulted in crashes with some compiler versions/optimizations, mainly in flockfile prior to pthread_create. 2011-07-30 08:02:14 -04:00			`if (f->lockcount == LONG_MAX)`
implement flockfile api, rework stdio locking 2011-03-12 21:55:45 -05:00			`return -1;`
			`f->lockcount++;`
			`return 0;`
			`}`
add proper fuxed-based locking for stdio previously, stdio used spinlocks, which would be unacceptable if we ever add support for thread priorities, and which yielded pathologically bad performance if an application attempted to use flockfile on a key file as a major/primary locking mechanism. i had held off on making this change for fear that it would hurt performance in the non-threaded case, but actually support for recursive locking had already inflicted that cost. by having the internal locking functions store a flag indicating whether they need to perform unlocking, rather than using the actual recursive lock counter, i was able to combine the conditionals at unlock time, eliminating any additional cost, and also avoid a nasty corner case where a huge number of calls to ftrylockfile could cause deadlock later at the point of internal locking. this commit also fixes some issues with usage of pthread_self conflicting with __attribute__((const)) which resulted in crashes with some compiler versions/optimizations, mainly in flockfile prior to pthread_create. 2011-07-30 08:02:14 -04:00			`if (f->lock < 0) f->lock = 0;`
simplify and optimize FILE lock handling 2011-03-24 23:16:52 -04:00			`if (f->lock \|\| a_cas(&f->lock, 0, tid))`
implement flockfile api, rework stdio locking 2011-03-12 21:55:45 -05:00			`return -1;`
			`f->lockcount = 1;`
			`return 0;`
			`}`