From 63ed3e92a93db5d5076a050b2288f3503183e68c Mon Sep 17 00:00:00 2001 From: green Date: Fri, 23 Feb 2001 04:59:12 +0000 Subject: Fix the problems I (and others, undoubtedly) have been having for a while with threaded software in -CURRENT acting very "weird". It has seemed, for example, in Mozilla that threads attempting to do host lookups have been locking up. That's exactly the case. There was a race condition in the implementation of the initialization of the mutex used to protect FILE operations, first of all: multiple instances of FLOCKFILE() in libc could occur on the same FILE at the same time and cause strange behavior by overwriting eachothers' creation of the mutex and the rest of the file lock. Secondly, it's not appropriate to test the "validity" of the file descriptor referenced by the FILE; if the code is calling FLOCKFILE() or FUNLOCKFILE(), it wants the FILE to be locked or unlocked, not to be locked or unlocked on the condition that _file is >= 0. This also could quite easily cause leaks by failing to perform the lock or unlock operation when it actually is needed. Mozilla now works again on -CURRENT when linked to libc_r.so.5 and libc.so.5. --- lib/libc/stdio/_flock_stub.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) (limited to 'lib') diff --git a/lib/libc/stdio/_flock_stub.c b/lib/libc/stdio/_flock_stub.c index a77fad9..a947398 100644 --- a/lib/libc/stdio/_flock_stub.c +++ b/lib/libc/stdio/_flock_stub.c @@ -83,6 +83,7 @@ struct __file_lock { static int init_lock(FILE *fp) { + static pthread_mutex_t init_lock_mutex = PTHREAD_MUTEX_INITIALIZER; struct __file_lock *p; int ret; @@ -92,7 +93,16 @@ init_lock(FILE *fp) p->fl_mutex = PTHREAD_MUTEX_INITIALIZER; p->fl_owner = NULL; p->fl_count = 0; + if (pthread_mutex_lock(&init_lock_mutex) != 0) { + free(p); + return (-1); + } + if (fp->_lock != NULL) { /* lost the race */ + free(p); + return (0); + } fp->_lock = p; + pthread_mutex_unlock(&init_lock_mutex); ret = 0; } return (ret); @@ -142,8 +152,7 @@ _ftrylockfile(FILE *fp) * Check if this is a real file with a valid lock, creating * the lock if needed: */ - if ((fp->_file >= 0) && - ((fp->_lock != NULL) || (init_lock(fp) == 0))) { + if (((fp->_lock != NULL) || (init_lock(fp) == 0))) { if (fp->_lock->fl_owner == curthread) fp->_lock->fl_count++; /* @@ -171,7 +180,7 @@ _funlockfile(FILE *fp) * Check if this is a real file with a valid lock owned * by the current thread: */ - if ((fp->_file >= 0) && (fp->_lock != NULL) && + if ((fp->_lock != NULL) && (fp->_lock->fl_owner == curthread)) { /* * Check if this thread has locked the FILE -- cgit v1.1