Add condvars and events via parking lot

lib/condvar.c

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: ISC
+
+#include <zinnia/atomic.h>
+#include <zinnia/condvar.h>
+#include <zinnia/park.h>
+#include <stdint.h>
+
+void condvar_init(struct condvar* cv) {
+    atomic_store(&cv->seq, 0, ATOMIC_RELAXED);
+    atomic_store(&cv->waiters, 0, ATOMIC_RELAXED);
+}
+
+void condvar_wait(struct condvar* cv, mutex_t* mutex) {
+    atomic_fetch_add(&cv->waiters, 1, ATOMIC_SEQ_CST);
+    uint32_t seq = atomic_load(&cv->seq, ATOMIC_SEQ_CST);
+    mutex_unlock(mutex);
+    park_wait(&cv->seq, seq);
+    atomic_fetch_sub(&cv->waiters, 1, ATOMIC_RELAXED);
+    mutex_lock(mutex);
+}
+
+static void wake(struct condvar* cv, size_t count) {
+    atomic_fetch_add(&cv->seq, 1, ATOMIC_SEQ_CST);
+    if (atomic_load(&cv->waiters, ATOMIC_SEQ_CST) != 0)
+        park_wake(&cv->seq, count);
+}
+
+void condvar_signal(struct condvar* cv) {
+    wake(cv, 1);
+}
+
+void condvar_broadcast(struct condvar* cv) {
+    wake(cv, SIZE_MAX);
+}