Plumbing for promise integration.

clients/c/promise.c

@@ -0,0 +1,86 @@
+#include <assert.h>
+#include <pthread.h>
+#include <stdlib.h>
+
+#include "promise.h"
+
+struct promise {
+  bool will_wait;
+  promise_callback on_success;
+  promise_callback on_failure;
+  void *passthrough;
+
+  bool fulfilled;
+  pthread_mutex_t lock;
+  pthread_cond_t cond;
+
+  bool success;
+  void *result;
+};
+
+promise *promise_create(bool will_wait, promise_callback on_success, promise_callback on_failure, void *passthrough) {
+  promise *promise_obj = malloc(sizeof(*promise_obj));
+  promise_obj->will_wait = will_wait;
+  promise_obj->on_success = on_success;
+  promise_obj->on_failure = on_failure;
+  promise_obj->passthrough = passthrough;
+
+  promise_obj->fulfilled = false;
+  assert(!pthread_mutex_init(&promise_obj->lock, NULL));
+  assert(!pthread_cond_init(&promise_obj->cond, NULL));
+  return promise_obj;
+}
+
+static void promise_destroy(promise *promise_obj) {
+  assert(!pthread_mutex_destroy(&promise_obj->lock));
+  assert(!pthread_cond_destroy(&promise_obj->cond));
+  free(promise_obj);
+}
+
+bool promise_wait(promise *promise_obj, void **result) {
+  assert(!pthread_mutex_lock(&promise_obj->lock));
+  assert(promise_obj->will_wait);
+  while (!promise_obj->fulfilled) {
+    pthread_cond_wait(&promise_obj->cond, &promise_obj->lock);
+  }
+  assert(!pthread_mutex_unlock(&promise_obj->lock));
+
+  // promise_obj is now filled in, and owned solely by us.
+  bool success = promise_obj->success;
+  if (result) {
+    *result = promise_obj->result;
+  }
+  promise_destroy(promise_obj);
+  return success;
+}
+
+void promise_complete(promise *promise_obj, void *result, bool success) {
+  assert(!pthread_mutex_lock(&promise_obj->lock));
+
+  if (success && promise_obj->on_success) {
+    promise_obj->on_success(promise_obj->passthrough, result);
+  } else if (!success && promise_obj->on_failure) {
+    promise_obj->on_failure(promise_obj->passthrough, result);
+  }
+
+  if (promise_obj->will_wait) {
+    // We don't own promise_obj; pass to promise_wait()
+    promise_obj->result = result;
+    promise_obj->success = success;
+    promise_obj->fulfilled = true;
+    assert(!pthread_cond_signal(&promise_obj->cond));
+    assert(!pthread_mutex_unlock(&promise_obj->lock));
+  } else {
+    // We own promise_obj
+    assert(!pthread_mutex_unlock(&promise_obj->lock));
+    promise_destroy(promise_obj);
+  }
+}
+
+void promise_succeed(promise *promise_obj, void *result) {
+  promise_complete(promise_obj, result, true);
+}
+
+void promise_fail(promise *promise_obj, void *result) {
+  promise_complete(promise_obj, result, false);
+}