aboutsummaryrefslogtreecommitdiff
path: root/linuxthreads/rwlock.c
diff options
context:
space:
mode:
authorUlrich Drepper <drepper@redhat.com>2000-01-12 11:39:14 +0000
committerUlrich Drepper <drepper@redhat.com>2000-01-12 11:39:14 +0000
commitce75c139ac162cf8d7d4a7598503bc3592328b2c (patch)
tree604f258eac5abfa916634aa002e6fd6bcc35fa82 /linuxthreads/rwlock.c
parent2e8048e533cf8f9ce23400c261cd8528cf37af5e (diff)
downloadglibc-ce75c139ac162cf8d7d4a7598503bc3592328b2c.zip
glibc-ce75c139ac162cf8d7d4a7598503bc3592328b2c.tar.gz
glibc-ce75c139ac162cf8d7d4a7598503bc3592328b2c.tar.bz2
Update.
2000-01-12 Ulrich Drepper <drepper@cygnus.com> * iconvdata/gconv-modules: Add aliases ISO-IR-199 and ISO-IR-203. Reported by Bruno Haible <haible@ilog.fr>. 2000-01-11 Andreas Schwab <schwab@suse.de> * sysdeps/i386/fpu/libm-test-ulps: Adjust some epsilons. 2000-01-10 Thorsten Kukuk <kukuk@suse.de> * nss/getent.c: Add ipv6 support for hosts. 2000-01-05 Philip Blundell <pb@futuretv.com> * sysdeps/unix/sysv/linux/arm/Versions: Add getrlimit, setrlimit, getrlimit64, setrlimit64 for GLIBC_2.1.3. * sysdeps/unix/sysv/linux/arm/syscalls.list: Add oldgetrlimit, oldsetrlimit. * sysdeps/unix/sysv/linux/arm/oldsetrlimit64.c: New file. * sysdeps/unix/sysv/linux/arm/oldgetrlimit64.c: Likewise. * sysdeps/unix/sysv/linux/arm/setrlimit64.c: Likewise. * sysdeps/unix/sysv/linux/arm/getrlimit64.c: Likewise. * sysdeps/unix/sysv/linux/arm/setrlimit.c: Likewise. * sysdeps/unix/sysv/linux/arm/getrlimit.c: Likewise. * sysdeps/unix/sysv/linux/arm/Makefile [subdir=resource] (sysdep_routines): Add oldgetrlimit64, oldsetrlimit64. [subdir=misc] (sysdep_headers): Add sys/elf.h. 2000-01-09 Andreas Jaeger <aj@suse.de> * manual/install.texi (Tools for Compilation): Update required compiler version. (Configuring and compiling): Restore old comments about configparms; modify to reflect current usage. 2000-01-09 Philip Blundell <philb@gnu.org> * sysdeps/posix/getaddrinfo.c (gaih_inet): Don't attempt name resolution if the hints included AI_NUMERICHOST.
Diffstat (limited to 'linuxthreads/rwlock.c')
-rw-r--r--linuxthreads/rwlock.c246
1 files changed, 228 insertions, 18 deletions
diff --git a/linuxthreads/rwlock.c b/linuxthreads/rwlock.c
index 1d78b78..7b472e2 100644
--- a/linuxthreads/rwlock.c
+++ b/linuxthreads/rwlock.c
@@ -1,5 +1,5 @@
/* Read-write lock implementation.
- Copyright (C) 1998 Free Software Foundation, Inc.
+ Copyright (C) 1998, 2000 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Xavier Leroy <Xavier.Leroy@inria.fr>
and Ulrich Drepper <drepper@cygnus.com>, 1998.
@@ -21,11 +21,167 @@
#include <errno.h>
#include <pthread.h>
+#include <stdlib.h>
#include "internals.h"
#include "queue.h"
#include "spinlock.h"
#include "restart.h"
+/*
+ * Check whether the calling thread already owns one or more read locks on the
+ * specified lock. If so, return a pointer to the read lock info structure
+ * corresponding to that lock.
+ */
+
+static pthread_readlock_info *
+rwlock_is_in_list(pthread_descr self, pthread_rwlock_t *rwlock)
+{
+ pthread_readlock_info *info;
+
+ for (info = self->p_readlock_list; info != NULL; info = info->pr_next)
+ {
+ if (info->pr_lock == rwlock)
+ return info;
+ }
+
+ return NULL;
+}
+
+/*
+ * Add a new lock to the thread's list of locks for which it has a read lock.
+ * A new info node must be allocated for this, which is taken from the thread's
+ * free list, or by calling malloc. If malloc fails, a null pointer is
+ * returned. Otherwise the lock info structure is initialized and pushed
+ * onto the thread's list.
+ */
+
+static pthread_readlock_info *
+rwlock_add_to_list(pthread_descr self, pthread_rwlock_t *rwlock)
+{
+ pthread_readlock_info *info = self->p_readlock_free;
+
+ if (info != NULL)
+ self->p_readlock_free = info->pr_next;
+ else
+ info = malloc(sizeof *info);
+
+ if (info == NULL)
+ return NULL;
+
+ info->pr_lock_count = 1;
+ info->pr_lock = rwlock;
+ info->pr_next = self->p_readlock_list;
+ self->p_readlock_list = info;
+
+ return info;
+}
+
+/*
+ * If the thread owns a read lock over the given pthread_rwlock_t,
+ * and this read lock is tracked in the thread's lock list,
+ * this function returns a pointer to the info node in that list.
+ * It also decrements the lock count within that node, and if
+ * it reaches zero, it removes the node from the list.
+ * If nothing is found, it returns a null pointer.
+ */
+
+static pthread_readlock_info *
+rwlock_remove_from_list(pthread_descr self, pthread_rwlock_t *rwlock)
+{
+ pthread_readlock_info **pinfo;
+
+ for (pinfo = &self->p_readlock_list; *pinfo != NULL; pinfo = &(*pinfo)->pr_next)
+ {
+ if ((*pinfo)->pr_lock == rwlock)
+ {
+ pthread_readlock_info *info = *pinfo;
+ if (--info->pr_lock_count == 0)
+ *pinfo = info->pr_next;
+ return info;
+ }
+ }
+
+ return NULL;
+}
+
+/*
+ * This function checks whether the conditions are right to place a read lock.
+ * It returns 1 if so, otherwise zero. The rwlock's internal lock must be
+ * locked upon entry.
+ */
+
+static int
+rwlock_can_rdlock(pthread_rwlock_t *rwlock, int have_lock_already)
+{
+ /* Can't readlock; it is write locked. */
+ if (rwlock->__rw_writer != NULL)
+ return 0;
+
+ /* Lock prefers readers; get it. */
+ if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP)
+ return 1;
+
+ /* Lock prefers writers, but none are waiting. */
+ if (queue_is_empty(&rwlock->__rw_write_waiting))
+ return 1;
+
+ /* Writers are waiting, but this thread already has a read lock */
+ if (have_lock_already)
+ return 1;
+
+ /* Writers are waiting, and this is a new lock */
+ return 0;
+}
+
+/*
+ * This function helps support brain-damaged recursive read locking
+ * semantics required by Unix 98, while maintaining write priority.
+ * This basically determines whether this thread already holds a read lock
+ * already. It returns 1 if so, otherwise it returns 0.
+ *
+ * If the thread has any ``untracked read locks'' then it just assumes
+ * that this lock is among them, just to be safe, and returns 1.
+ *
+ * Also, if it finds the thread's lock in the list, it sets the pointer
+ * referenced by pexisting to refer to the list entry.
+ *
+ * If the thread has no untracked locks, and the lock is not found
+ * in its list, then it is added to the list. If this fails,
+ * then *pout_of_mem is set to 1.
+ */
+
+static int
+rwlock_have_already(pthread_descr *pself, pthread_rwlock_t *rwlock,
+ pthread_readlock_info **pexisting, int *pout_of_mem)
+{
+ pthread_readlock_info *existing = NULL;
+ int out_of_mem = 0, have_lock_already = 0;
+ pthread_descr self = *pself;
+
+ if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_WRITER_NP)
+ {
+ if (!self)
+ self = thread_self();
+
+ existing = rwlock_is_in_list(self, rwlock);
+
+ if (existing != NULL || self->p_untracked_readlock_count > 0)
+ have_lock_already = 1;
+ else
+ {
+ existing = rwlock_add_to_list(self, rwlock);
+ if (existing == NULL)
+ out_of_mem = 1;
+ }
+ }
+
+ *pout_of_mem = out_of_mem;
+ *pexisting = existing;
+ *pself = self;
+
+ return have_lock_already;
+}
+
int
pthread_rwlock_init (pthread_rwlock_t *rwlock,
const pthread_rwlockattr_t *attr)
@@ -68,24 +224,26 @@ pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
return 0;
}
-
int
pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
pthread_descr self = NULL;
+ pthread_readlock_info *existing;
+ int out_of_mem, have_lock_already;
- while (1)
+ have_lock_already = rwlock_have_already(&self, rwlock,
+ &existing, &out_of_mem);
+
+ for (;;)
{
+ if (self == NULL)
+ self = thread_self ();
+
__pthread_lock (&rwlock->__rw_lock, self);
- if (rwlock->__rw_writer == NULL
- || (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
- && rwlock->__rw_readers != 0))
- /* We can add a reader lock. */
+
+ if (rwlock_can_rdlock(rwlock, have_lock_already))
break;
- /* Suspend ourselves, then try again */
- if (self == NULL)
- self = thread_self ();
enqueue (&rwlock->__rw_read_waiting, self);
__pthread_unlock (&rwlock->__rw_lock);
suspend (self); /* This is not a cancellation point */
@@ -94,26 +252,56 @@ pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
++rwlock->__rw_readers;
__pthread_unlock (&rwlock->__rw_lock);
+ if (have_lock_already || out_of_mem)
+ {
+ if (existing != NULL)
+ existing->pr_lock_count++;
+ else
+ self->p_untracked_readlock_count++;
+ }
+
return 0;
}
-
int
pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
- int result = EBUSY;
+ pthread_descr self = thread_self();
+ pthread_readlock_info *existing;
+ int out_of_mem, have_lock_already;
+ int retval = EBUSY;
- __pthread_lock (&rwlock->__rw_lock, NULL);
- if (rwlock->__rw_writer == NULL
- || (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
- && rwlock->__rw_readers != 0))
+ have_lock_already = rwlock_have_already(&self, rwlock,
+ &existing, &out_of_mem);
+
+ __pthread_lock (&rwlock->__rw_lock, self);
+
+ /* 0 is passed to here instead of have_lock_already.
+ This is to meet Single Unix Spec requirements:
+ if writers are waiting, pthread_rwlock_tryrdlock
+ does not acquire a read lock, even if the caller has
+ one or more read locks already. */
+
+ if (rwlock_can_rdlock(rwlock, 0))
{
++rwlock->__rw_readers;
- result = 0;
+ retval = 0;
}
+
__pthread_unlock (&rwlock->__rw_lock);
- return result;
+ if (retval == 0)
+ {
+ if (have_lock_already || out_of_mem)
+ {
+ if (existing != NULL)
+ existing->pr_lock_count++;
+ else
+ self->p_untracked_readlock_count++;
+ }
+ }
+
+ return retval;
}
@@ -210,6 +398,28 @@ pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
__pthread_unlock (&rwlock->__rw_lock);
if (th != NULL)
restart (th);
+
+ /* Recursive lock fixup */
+
+ if (rwlock->__rw_kind == PTHREAD_RWLOCK_PREFER_WRITER_NP)
+ {
+ pthread_descr self = thread_self();
+ pthread_readlock_info *victim = rwlock_remove_from_list(self, rwlock);
+
+ if (victim != NULL)
+ {
+ if (victim->pr_lock_count == 0)
+ {
+ victim->pr_next = self->p_readlock_free;
+ self->p_readlock_free = victim;
+ }
+ }
+ else
+ {
+ if (self->p_untracked_readlock_count > 0)
+ self->p_untracked_readlock_count--;
+ }
+ }
}
return 0;