Rich Felker
dba68bf98f
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.
19 lines
330 B
C
19 lines
330 B
C
#include "stdio_impl.h"
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#include "pthread_impl.h"
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int ftrylockfile(FILE *f)
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{
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int tid = pthread_self()->tid;
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if (f->lock == tid) {
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if (f->lockcount == LONG_MAX)
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return -1;
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f->lockcount++;
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return 0;
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}
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if (f->lock < 0) f->lock = 0;
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if (f->lock || a_cas(&f->lock, 0, tid))
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return -1;
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f->lockcount = 1;
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return 0;
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}
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