Changeset: f1e2746a546e for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/f1e2746a546e
Modified Files:
gdk/gdk_system.h
Branch: Jul2021
Log Message:
Work around a bug in the pthreads implementation of read-write locks.
There is a potential deadlock situation in the implementation of the
two "try" functions pthread_rwlock_tryrdlock and
pthread_rwlock_trywrlock which was fixed in version 2.30.
diffs (92 lines):
diff --git a/gdk/gdk_system.h b/gdk/gdk_system.h
--- a/gdk/gdk_system.h
+++ b/gdk/gdk_system.h
@@ -439,6 +439,8 @@ typedef struct MT_Lock {
pthread_mutex_destroy(&(l)->lock); \
} while (0)
+#if !defined(__GLIBC__) || __GLIBC__ > 2 || (__GLIBC__ == 2 &&
defined(__GLIBC_MINOR__) && __GLIBC_MINOR__ >= 30)
+/* this is the normal implementation of our pthreads-based read-write lock */
typedef struct MT_RWLock {
pthread_rwlock_t lock;
char name[MT_NAME_LEN];
@@ -465,6 +467,79 @@ typedef struct MT_RWLock {
#define MT_rwlock_wrunlock(l) pthread_rwlock_unlock(&(l)->lock)
+#else
+/* in glibc before 2.30, there was a deadlock condition in the tryrdlock
+ * and trywrlock functions, we work around that by not using the
+ * implementation at all
+ * see https://sourceware.org/bugzilla/show_bug.cgi?id=23844 for a
+ * discussion and comment 14 for the analysis */
+typedef struct MT_RWLock {
+ pthread_mutex_t lock;
+ ATOMIC_TYPE readers;
+ char name[MT_NAME_LEN];
+} MT_RWLock;
+
+#define MT_RWLOCK_INITIALIZER(n) \
+ { .lock = PTHREAD_MUTEX_INITIALIZER, .readers = ATOMIC_VAR_INIT(0),
.name = #n, }
+
+#define MT_rwlock_init(l, n) \
+ do { \
+ pthread_mutex_init(&(l)->lock, 0); \
+ ATOMIC_INIT(&(l)->readers, 0); \
+ strcpy_len((l)->name, (n), sizeof((l)->name)); \
+ } while (0)
+
+#define MT_rwlock_destroy(l) \
+ do { \
+ pthread_mutex_destroy(&(l)->lock); \
+ ATOMIC_DESTROY(&(l)->readers); \
+ } while (0)
+
+#define MT_rwlock_rdlock(l) \
+ do { \
+ pthread_mutex_lock(&(l)->lock); \
+ (void) ATOMIC_INC(&(l)->readers); \
+ pthread_mutex_unlock(&(l)->lock); \
+ } while (0)
+
+static inline bool
+MT_rwlock_rdtry(MT_RWLock *l)
+{
+ if (pthread_mutex_trylock(&l->lock) != 0)
+ return false;
+ (void) ATOMIC_INC(&(l)->readers);
+ pthread_mutex_unlock(&l->lock);
+ return true;
+}
+
+#define MT_rwlock_rdunlock(l) \
+ do { \
+ (void) ATOMIC_DEC(&(l)->readers); \
+ } while (0)
+
+#define MT_rwlock_wrlock(l) \
+ do { \
+ pthread_mutex_lock(&(l)->lock); \
+ while (ATOMIC_GET(&(l)->readers) > 0) \
+ MT_sleep_ms(1); \
+ } while (0)
+
+static inline bool
+MT_rwlock_wrtry(MT_RWLock *l)
+{
+ if (pthread_mutex_trylock(&l->lock) != 0)
+ return false;
+ if (ATOMIC_GET(&l->readers) > 0) {
+ pthread_mutex_unlock(&l->lock);
+ return false;
+ }
+ return true;
+}
+
+#define MT_rwlock_wrunlock(l) pthread_mutex_unlock(&(l)->lock);
+
+#endif
+
#endif
#ifdef LOCK_STATS
_______________________________________________
checkin-list mailing list
checkin-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/checkin-list
