From 8d7fbf911acbd4620135efc34cdc793ad529e3d5 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Sun, 21 Mar 2021 23:57:01 +0100
Subject: [PATCH] Added a simple layer for semaphores

---
 lib/coro.h              | 12 ++++++++++++
 sysdep/unix/coroutine.c | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/lib/coro.h b/lib/coro.h
index 51712b36..c1f4ce47 100644
--- a/lib/coro.h
+++ b/lib/coro.h
@@ -22,5 +22,17 @@ struct coroutine;
  */
 struct coroutine *coro_run(pool *, void (*entry)(void *), void *data);
 
+/* Semaphores are handy to sleep and wake worker threads. */
+struct bsem;
+
+/* Create a semaphore. Be sure to choose such a pool that happens to be freed
+ * only when the semaphore can't be waited for or posted. */
+struct bsem *bsem_new(pool *);
+
+/* Post a semaphore (wake the worker). */
+void bsem_post(struct bsem *);
+
+/* Wait for a semaphore. Never do this within a locked context. */
+void bsem_wait(struct bsem *);
 
 #endif
diff --git a/sysdep/unix/coroutine.c b/sysdep/unix/coroutine.c
index bf5b09db..febf0511 100644
--- a/sysdep/unix/coroutine.c
+++ b/sysdep/unix/coroutine.c
@@ -173,3 +173,43 @@ struct coroutine *coro_run(pool *p, void (*entry)(void *), void *data)
 
   return c;
 }
+
+/* Semaphores */
+struct bsem {
+  resource r;
+  sem_t sem;
+};
+
+static void bsem_free(resource *r)
+{
+  struct bsem *b = (void *) r;
+  if (sem_destroy(&b->sem) < 0)
+    bug("sem_destroy() failed: %m");
+}
+
+static struct resclass bsem_class = {
+  .name = "Semaphore",
+  .size = sizeof(struct bsem),
+  .free = bsem_free,
+};
+
+struct bsem *bsem_new(pool *p) {
+  struct bsem *b = ralloc(p, &bsem_class);
+  if (sem_init(&b->sem, 0, 0) < 0)
+    bug("sem_init() failed: %m");
+
+  return b;
+}
+
+void bsem_post(struct bsem *b) {
+  if (sem_post(&b->sem) < 0)
+    bug("sem_post() failed: %m");
+}
+
+void bsem_wait(struct bsem *b) {
+  if (sem_wait(&b->sem) < 0)
+    if (errno == EINTR)
+      return bsem_wait(b);
+    else
+      bug("sem_wait() failed: %m");
+}