Refcount grpc_alarm object so that grpc_alarm_destroy can safely be called before the alarm event is dequeued from the completion queue

3 files changed, 105 insertions, 8 deletions

diff --git a/src/core/lib/surface/alarm.c b/src/core/lib/surface/alarm.c
index ef8405cca8..343e48c101 100644
--- a/src/core/lib/surface/alarm.c
+++ b/src/core/lib/surface/alarm.c
@@ -15,13 +15,19 @@
  * limitations under the License.
  *
  */
+#include "src/core/lib/surface/alarm_internal.h"
 
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include "src/core/lib/iomgr/timer.h"
 #include "src/core/lib/surface/completion_queue.h"
 
+#ifndef NDEBUG
+grpc_tracer_flag grpc_trace_alarm_refcount = GRPC_TRACER_INITIALIZER(false);
+#endif
+
 struct grpc_alarm {
+  gpr_refcount refs;
   grpc_timer alarm;
   grpc_closure on_alarm;
   grpc_cq_completion completion;
@@ -31,13 +37,58 @@ struct grpc_alarm {
   void *tag;
 };
 
-static void do_nothing_end_completion(grpc_exec_ctx *exec_ctx, void *arg,
-                                      grpc_cq_completion *c) {}
+static void alarm_ref(grpc_alarm *alarm) { gpr_ref(&alarm->refs); }
+
+static void alarm_unref(grpc_alarm *alarm) {
+  if (gpr_unref(&alarm->refs)) {
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    GRPC_CQ_INTERNAL_UNREF(&exec_ctx, alarm->cq, "alarm");
+    grpc_exec_ctx_finish(&exec_ctx);
+    gpr_free(alarm);
+  }
+}
+
+#ifndef NDEBUG
+static void alarm_ref_dbg(grpc_alarm *alarm, const char *reason,
+                          const char *file, int line) {
+  if (GRPC_TRACER_ON(grpc_trace_alarm_refcount)) {
+    gpr_atm val = gpr_atm_no_barrier_load(&alarm->refs.count);
+    gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
+            "Alarm:%p  ref %" PRIdPTR " -> %" PRIdPTR " %s", alarm, val,
+            val + 1, reason);
+  }
+
+  alarm_ref(alarm);
+}
+
+static void alarm_unref_dbg(grpc_alarm *alarm, const char *reason,
+                            const char *file, int line) {
+  if (GRPC_TRACER_ON(grpc_trace_alarm_refcount)) {
+    gpr_atm val = gpr_atm_no_barrier_load(&alarm->refs.count);
+    gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
+            "Alarm:%p  Unref %" PRIdPTR " -> %" PRIdPTR " %s", alarm, val,
+            val - 1, reason);
+  }
+
+  alarm_unref(alarm);
+}
+#endif
+
+static void alarm_end_completion(grpc_exec_ctx *exec_ctx, void *arg,
+                                 grpc_cq_completion *c) {
+  grpc_alarm *alarm = arg;
+  GRPC_ALARM_UNREF(alarm, "dequeue-end-op");
+}
 
 static void alarm_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
   grpc_alarm *alarm = arg;
-  grpc_cq_end_op(exec_ctx, alarm->cq, alarm->tag, error,
-                 do_nothing_end_completion, NULL, &alarm->completion);
+
+  /* We are queuing an op on completion queue. This means, the alarm's structure
+     cannot be destroyed until the op is dequeued. Adding an extra ref
+     here and unref'ing when the op is dequeued will achieve this */
+  GRPC_ALARM_REF(alarm, "queue-end-op");
+  grpc_cq_end_op(exec_ctx, alarm->cq, alarm->tag, error, alarm_end_completion,
+                 (void *)alarm, &alarm->completion);
 }
 
 grpc_alarm *grpc_alarm_create(grpc_completion_queue *cq, gpr_timespec deadline,
@@ -45,6 +96,14 @@ grpc_alarm *grpc_alarm_create(grpc_completion_queue *cq, gpr_timespec deadline,
   grpc_alarm *alarm = gpr_malloc(sizeof(grpc_alarm));
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
 
+  gpr_ref_init(&alarm->refs, 1);
+
+#ifndef NDEBUG
+  if (GRPC_TRACER_ON(grpc_trace_alarm_refcount)) {
+    gpr_log(GPR_DEBUG, "Alarm:%p created (ref: 1)", alarm);
+  }
+#endif
+
   GRPC_CQ_INTERNAL_REF(cq, "alarm");
   alarm->cq = cq;
   alarm->tag = tag;
@@ -66,9 +125,6 @@ void grpc_alarm_cancel(grpc_alarm *alarm) {
 }
 
 void grpc_alarm_destroy(grpc_alarm *alarm) {
-  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_alarm_cancel(alarm);
-  GRPC_CQ_INTERNAL_UNREF(&exec_ctx, alarm->cq, "alarm");
-  gpr_free(alarm);
-  grpc_exec_ctx_finish(&exec_ctx);
+  GRPC_ALARM_UNREF(alarm, "alarm_destroy");
 }
diff --git a/src/core/lib/surface/alarm_internal.h b/src/core/lib/surface/alarm_internal.h
new file mode 100644
index 0000000000..a9b0968e34
--- /dev/null
+++ b/src/core/lib/surface/alarm_internal.h
@@ -0,0 +1,39 @@
+/*
+ *
+ * Copyright 2015-2017 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_SURFACE_ALARM_INTERNAL_H
+#define GRPC_CORE_LIB_SURFACE_ALARM_INTERNAL_H
+
+#include <grpc/support/log.h>
+#include "src/core/lib/debug/trace.h"
+
+#ifndef NDEBUG
+
+extern grpc_tracer_flag grpc_trace_alarm_refcount;
+#define GRPC_ALARM_REF(a, reason) alarm_ref_dbg(a, reason, __FILE__, __LINE__)
+#define GRPC_ALARM_UNREF(a, reason) \
+  alarm_unref_dbg(a, reason, __FILE__, __LINE__)
+
+#else /* !defined(NDEBUG) */
+
+#define GRPC_ALARM_REF(a, reason) alarm_ref(a)
+#define GRPC_ALARM_UNREF(a, reason) alarm_unref(a)
+
+#endif /* defined(NDEBUG) */
+
+#endif  // GRPC_CORE_LIB_SURFACE_ALARM_INTERNAL_H
diff --git a/src/core/lib/surface/init.c b/src/core/lib/surface/init.c
index 14a86bfa0a..7a5f398c96 100644
--- a/src/core/lib/surface/init.c
+++ b/src/core/lib/surface/init.c
@@ -36,6 +36,7 @@
 #include "src/core/lib/iomgr/resource_quota.h"
 #include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/slice/slice_internal.h"
+#include "src/core/lib/surface/alarm_internal.h"
 #include "src/core/lib/surface/api_trace.h"
 #include "src/core/lib/surface/call.h"
 #include "src/core/lib/surface/channel_init.h"
@@ -137,6 +138,7 @@ void grpc_init(void) {
     grpc_register_tracer("call_error", &grpc_call_error_trace);
 #ifndef NDEBUG
     grpc_register_tracer("pending_tags", &grpc_trace_pending_tags);
+    grpc_register_tracer("alarm_refcount", &grpc_trace_alarm_refcount);
     grpc_register_tracer("queue_refcount", &grpc_trace_cq_refcount);
     grpc_register_tracer("closure", &grpc_trace_closure);
     grpc_register_tracer("error_refcount", &grpc_trace_error_refcount);