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https://github.com/fluencelabs/musl
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c21f750727
instead of using a waiters count, add a bit to the lock field indicating that the lock may have waiters. threads which obtain the lock after contending for it will perform a potentially-spurious wake when they release the lock.
44 lines
985 B
C
44 lines
985 B
C
#include "stdio_impl.h"
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#include "pthread_impl.h"
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#include <limits.h>
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#define MAYBE_WAITERS 0x40000000
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void __do_orphaned_stdio_locks()
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{
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FILE *f;
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for (f=__pthread_self()->stdio_locks; f; f=f->next_locked)
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a_store(&f->lock, 0x40000000);
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}
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void __unlist_locked_file(FILE *f)
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{
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if (f->lockcount) {
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if (f->next_locked) f->next_locked->prev_locked = f->prev_locked;
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if (f->prev_locked) f->prev_locked->next_locked = f->next_locked;
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else __pthread_self()->stdio_locks = f->next_locked;
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}
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}
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int ftrylockfile(FILE *f)
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{
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pthread_t self = __pthread_self();
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int tid = self->tid;
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int owner = f->lock;
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if ((owner & ~MAYBE_WAITERS) == 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 (owner < 0) f->lock = owner = 0;
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if (owner || a_cas(&f->lock, 0, tid))
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return -1;
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f->lockcount = 1;
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f->prev_locked = 0;
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f->next_locked = self->stdio_locks;
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if (f->next_locked) f->next_locked->prev_locked = f;
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self->stdio_locks = f;
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return 0;
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}
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