[T106][ZXW-22]7520V3SCV2.01.01.02P42U09_VEC_V0.8_AP_VEC origin source commit
Change-Id: Ic6e05d89ecd62fc34f82b23dcf306c93764aec4b
diff --git a/ap/libc/glibc/glibc-2.22/nptl/DESIGN-rwlock.txt b/ap/libc/glibc/glibc-2.22/nptl/DESIGN-rwlock.txt
new file mode 100644
index 0000000..810d1b8
--- /dev/null
+++ b/ap/libc/glibc/glibc-2.22/nptl/DESIGN-rwlock.txt
@@ -0,0 +1,113 @@
+Reader Writer Locks pseudocode
+==============================
+
+ pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
+ pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
+ pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
+
+struct pthread_rwlock_t {
+
+ unsigned int lock:
+ - internal mutex
+
+ unsigned int writers_preferred;
+ - locking mode: 0 recursive, readers preferred
+ 1 nonrecursive, writers preferred
+
+ unsigned int readers;
+ - number of read-only references various threads have
+
+ pthread_t writer;
+ - descriptor of the writer or 0
+
+ unsigned int readers_wakeup;
+ - 'all readers should wake up' futex.
+
+ unsigned int writer_wakeup;
+ - 'one writer should wake up' futex.
+
+ unsigned int nr_readers_queued;
+ - number of readers queued up.
+
+ unsigned int nr_writers_queued;
+ - number of writers queued up.
+}
+
+pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
+{
+ lll_lock(rwlock->lock);
+ for (;;) {
+ if (!rwlock->writer && (!rwlock->nr_writers_queued ||
+ !rwlock->writers_preferred))
+ break;
+
+ rwlock->nr_readers_queued++;
+ val = rwlock->readers_wakeup;
+ lll_unlock(rwlock->lock);
+
+ futex_wait(&rwlock->readers_wakeup, val)
+
+ lll_lock(rwlock->lock);
+ rwlock->nr_readers_queued--;
+ }
+ rwlock->readers++;
+ lll_unlock(rwlock->lock);
+}
+
+pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
+{
+ int result = EBUSY;
+ lll_lock(rwlock->lock);
+ if (!rwlock->writer && (!rwlock->nr_writers_queued ||
+ !rwlock->writers_preferred))
+ rwlock->readers++;
+ lll_unlock(rwlock->lock);
+ return result;
+}
+
+pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
+{
+ lll_lock(rwlock->lock);
+ for (;;) {
+ if (!rwlock->writer && !rwlock->readers)
+ break;
+
+ rwlock->nr_writers_queued++;
+ val = rwlock->writer_wakeup;
+ lll_unlock(rwlock->lock);
+
+ futex_wait(&rwlock->writer_wakeup, val);
+
+ lll_lock(rwlock->lock);
+ rwlock->nr_writers_queued--;
+ }
+ rwlock->writer = pthread_self();
+ lll_unlock(rwlock->lock);
+}
+
+pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
+{
+ lll_lock(rwlock->lock);
+
+ if (rwlock->writer)
+ rwlock->writer = 0;
+ else
+ rwlock->readers--;
+
+ if (!rwlock->readers) {
+ if (rwlock->nr_writers_queued) {
+ ++rwlock->writer_wakeup;
+ lll_unlock(rwlock->lock);
+ futex_wake(&rwlock->writer_wakeup, 1);
+ return;
+ } else
+ if (rwlock->nr_readers_queued) {
+ ++rwlock->readers_wakeup;
+ lll_unlock(rwlock->lock);
+ futex_wake(&rwlock->readers_wakeup, MAX_INT);
+ return;
+ }
+ }
+
+ lll_unlock(rwlock->lock);
+}