MB-42657: Don't call shutdown_server from signal handler

shutdown_server isn't signal-safe. Instead we should just
set the memcached_shutdown variable to true as that is signal
safe.

The clock callback happens every second and will poll the
shutdown variable.

Note that the sigterm and sigint handler isn't the "normal" way
to initiate shutdown, that happens from:

  a) the parent process close stdin
  b) someone sends shutdown request

Change-Id: I7cbbe0028643d6fdf747bdd710572d9279403bc3
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/156471
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: trondn

daemon/mc_time.cc

@@ -188,8 +188,8 @@ static void mc_time_clock_event_handler(evutil_socket_t fd, short which, void *a
     t.tv_usec = 0;
 
     if (is_memcached_shutting_down()) {
-        event_base_loopbreak(event_get_base(&clockevent));
-        return ;
+        stop_memcached_main_base();
+        return;
     }
 
     if (initialized) {

daemon/mcbp_executors.cc

@@ -518,9 +518,11 @@ static void get_errmap_executor(Cookie& cookie) {
 
 static void shutdown_executor(Cookie& cookie) {
     if (session_cas.increment_session_counter(cookie.getRequest().getCas())) {
-        shutdown_server();
         session_cas.decrement_session_counter();
         cookie.sendResponse(cb::mcbp::Status::Success);
+        LOG_INFO("{} Shutdown server requested",
+                 cookie.getConnection().getId());
+        shutdown_server();
     } else {
         cookie.sendResponse(cb::mcbp::Status::KeyEexists);
     }

daemon/memcached.cc

@@ -80,6 +80,10 @@ bool is_memcached_shutting_down() {
     return memcached_shutdown;
 }
 
+void shutdown_server() {
+    memcached_shutdown = true;
+}
+
 /*
  * forward declarations
  */
@@ -95,7 +99,13 @@ struct stats stats;
 
 /** file scope variables **/
 
-static std::unique_ptr<folly::EventBase> main_base;
+std::unique_ptr<folly::EventBase> main_base;
+
+void stop_memcached_main_base() {
+    if (main_base) {
+        main_base->terminateLoopSoon();
+    }
+}
 
 static folly::Synchronized<std::string, std::mutex> reset_stats_time;
 /**
@@ -670,7 +680,7 @@ bool is_bucket_dying(Connection& c) {
 }
 
 static void sigint_handler() {
-    shutdown_server();
+    memcached_shutdown = true;
 }
 
 #ifdef WIN32
@@ -684,7 +694,7 @@ static void release_signal_handlers() {
 #else
 
 static void sigterm_handler(evutil_socket_t, short, void *) {
-    shutdown_server();
+    memcached_shutdown = true;
 }
 
 static struct event* sigterm_event;
@@ -715,28 +725,6 @@ const char* get_server_version() {
     return PRODUCT_VERSION;
 }
 
-static std::condition_variable shutdown_cv;
-static std::mutex shutdown_cv_mutex;
-static bool memcached_can_shutdown = false;
-void shutdown_server() {
-
-    std::unique_lock<std::mutex> lk(shutdown_cv_mutex);
-    if (!memcached_can_shutdown) {
-        // log and proceed to wait shutdown
-        LOG_INFO_RAW("shutdown_server waiting for can_shutdown signal");
-        shutdown_cv.wait(lk, []{return memcached_can_shutdown;});
-    }
-    memcached_shutdown = true;
-    LOG_INFO_RAW("Received shutdown request");
-    main_base->terminateLoopSoon();
-}
-
-void enable_shutdown() {
-    std::unique_lock<std::mutex> lk(shutdown_cv_mutex);
-    memcached_can_shutdown = true;
-    shutdown_cv.notify_all();
-}
-
 void cleanup_buckets() {
     for (auto &bucket : all_buckets) {
         bool waiting;
@@ -1032,13 +1020,6 @@ int memcached_main(int argc, char** argv) {
     startStaleTraceDumpRemover(std::chrono::minutes(1),
                                std::chrono::minutes(5));
 
-    /*
-     * MB-20034.
-     * Now that all threads have been created, e.g. the audit thread, threads
-     * associated with extensions and the workers, we can enable shutdown.
-     */
-    enable_shutdown();
-
     /* Initialise memcached time keeping */
     mc_time_init(main_base->getLibeventBase());
 

daemon/memcached.h

@@ -57,6 +57,7 @@ void scheduleDcpStep(Cookie& cookie);
 void safe_close(SOCKET sfd);
 const char* get_server_version();
 bool is_memcached_shutting_down();
+void stop_memcached_main_base();
 
 /**
  * Connection-related functions