diff options
| -rw-r--r-- | libfshelp/lock-acquire.c | 95 |
1 files changed, 77 insertions, 18 deletions
diff --git a/libfshelp/lock-acquire.c b/libfshelp/lock-acquire.c index 574bc5cb..06c93d8c 100644 --- a/libfshelp/lock-acquire.c +++ b/libfshelp/lock-acquire.c @@ -23,17 +23,30 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ #define EWOULDBLOCK EAGAIN /* XXX */ +/* Remove this when glibc has it. */ +#ifndef __LOCK_ATOMIC +#define __LOCK_ATOMIC 16 +#endif + error_t fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, int flags) { + int atomic = 0; + if (!(flags & (LOCK_UN | LOCK_EX | LOCK_SH))) return 0; if ((flags & LOCK_UN) && (flags & (LOCK_SH | LOCK_EX))) return EINVAL; - + + if (flags & __LOCK_ATOMIC) + { + atomic = 1; + flags &= ~__LOCK_ATOMIC; + } + if (flags & LOCK_EX) flags &= ~LOCK_SH; @@ -44,8 +57,10 @@ fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, if (*user & LOCK_UN) return 0; - assert (*user == box->type); - assert (*user == LOCK_SH || *user == LOCK_EX); + assert (*user == box->type || + (*user == LOCK_SH && box->type == (LOCK_SH | LOCK_EX))); + assert (*user == LOCK_SH || *user == LOCK_EX || + *user == (LOCK_SH | LOCK_EX)); if (*user == LOCK_SH) { @@ -60,12 +75,39 @@ fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, box->waiting = 0; pthread_cond_broadcast (&box->wait); } + if (box->type == (LOCK_SH | LOCK_EX) && box->shcount == 1 && box->waiting) + { + box->waiting = 0; + pthread_cond_broadcast (&box->wait); + } *user = LOCK_UN; } else { + if (atomic && *user == (flags & (LOCK_SH | LOCK_EX))) + /* Already have it the right way. */ + return 0; + + if (atomic && *user == LOCK_EX && flags & LOCK_SH) + { + /* Easy atomic change. */ + *user = LOCK_SH; + box->type = LOCK_SH; + box->shcount = 1; + if (box->waiting) + { + box->waiting = 0; + pthread_cond_broadcast (&box->wait); + } + return 0; + } + + /* We can not have two people upgrading their lock, this is a deadlock! */ + if (*user == LOCK_SH && atomic && box->type == (LOCK_SH | LOCK_EX)) + return EDEADLK; + /* If we have an exclusive lock, release it. */ - if (*user == LOCK_EX) + if (*user == LOCK_EX && !atomic) { *user = LOCK_UN; box->type = LOCK_UN; @@ -75,19 +117,9 @@ fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, pthread_cond_broadcast (&box->wait); } } - - /* If there is an exclusive lock, wait for it to end. */ - while (box->type == LOCK_EX) - { - if (flags & LOCK_NB) - return EWOULDBLOCK; - box->waiting = 1; - if (pthread_hurd_cond_wait_np (&box->wait, mut)) - return EINTR; - } /* If we have a shared lock, release it. */ - if (*user == LOCK_SH) + if (*user == LOCK_SH && !atomic) { *user = LOCK_UN; if (!--box->shcount) @@ -99,12 +131,29 @@ fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, pthread_cond_broadcast (&box->wait); } } + if (box->type == (LOCK_SH | LOCK_EX) && box->shcount == 1 && + box->waiting) + { + box->waiting = 0; + pthread_cond_broadcast (&box->wait); + } } - + + /* If there is another exclusive lock or a pending upgrade, wait for it to + end. */ + while (box->type & LOCK_EX) + { + if (flags & LOCK_NB) + return EWOULDBLOCK; + box->waiting = 1; + if (pthread_hurd_cond_wait_np (&box->wait, mut)) + return EINTR; + } + assert ((flags & LOCK_SH) || (flags & LOCK_EX)); if (flags & LOCK_SH) { - assert (box->type != LOCK_EX); + assert (!(box->type & LOCK_EX)); *user = LOCK_SH; box->type = LOCK_SH; box->shcount++; @@ -112,17 +161,27 @@ fshelp_acquire_lock (struct lock_box *box, int *user, pthread_mutex_t *mut, else if (flags & LOCK_EX) { /* Wait for any shared (and exclusive) locks to finish. */ - while (box->type != LOCK_UN) + while ((*user == LOCK_SH && box->shcount > 1) || + (*user == LOCK_UN && box->type != LOCK_UN)) { if (flags & LOCK_NB) return EWOULDBLOCK; else { + /* Tell others that we are upgrading. */ + if (*user == LOCK_SH && atomic) + box->type = LOCK_SH | LOCK_EX; + box->waiting = 1; if (pthread_hurd_cond_wait_np (&box->wait, mut)) return EINTR; } } + if (*user == LOCK_SH) + { + assert (box->shcount == 1); + box->shcount = 0; + } box->type = LOCK_EX; *user = LOCK_EX; } |