[alohalytics] Graceful FastCGI server stop on SIGTERM and SIGINT.

1 files changed, 30 insertions, 11 deletions

diff --git a/3party/Alohalytics/server/fcgi_server.cc b/3party/Alohalytics/server/fcgi_server.cc
index 3ee52ea799..fd29dba4b5 100644
--- a/3party/Alohalytics/server/fcgi_server.cc
+++ b/3party/Alohalytics/server/fcgi_server.cc
@@ -139,6 +139,17 @@ int main(int argc, char * argv[]) {
     ALOG("  - SIGHUP reopens main data file and SIGUSR1 reopens debug log file for logrotate utility.");
     return -1;
   }
+  int result = FCGX_Init();
+  if (0 != result) {
+    ALOG("ERROR: FCGX_Init has failed with code", result);
+    return result;
+  }
+  FCGX_Request request;
+  result = FCGX_InitRequest(&request, 0, FCGI_FAIL_ACCEPT_ON_INTR);
+  if (0 != result) {
+    ALOG("ERROR: FCGX_InitRequest has failed with code", result);
+    return result;
+  }
 
   // Redirect cout into a file if it was given in the command line.
   CoutToFileRedirector log_redirector(argc > 2 ? argv[2] : nullptr);
@@ -150,18 +161,26 @@ int main(int argc, char * argv[]) {
   if (SIG_ERR == ::signal(SIGUSR1, [](int) { gReceivedSIGUSR1 = SIGUSR1; })) {
     ATLOG("WARNING: Can't set SIGUSR1 handler. Logrotate will not work correctly.");
   }
-
-  int result = FCGX_Init();
-  if (0 != result) {
-    ALOG("ERROR: FCGX_Init has failed with code", result);
-    return result;
-  }
-  FCGX_Request request;
-  result = FCGX_InitRequest(&request, 0, FCGI_FAIL_ACCEPT_ON_INTR);
-  if (0 != result) {
-    ALOG("ERROR: FCGX_InitRequest has failed with code", result);
-    return result;
+  // NOTE: On most systems, when we get a signal, FCGX_Accept_r blocks even with a FCGI_FAIL_ACCEPT_ON_INTR flag set
+  // in the request. Looks like on these systems default signal function installs the signals with the SA_RESTART flag
+  // set (see man sigaction for more details) and syscalls are automatically restart themselves if a signal occurs.
+  // To "fix" this behavior and gracefully shutdown our server, we use a trick from
+  // W. Richard Stevens, Stephen A. Rago, "Advanced Programming in the UNIX Environment", 2nd edition, page 329.
+  // It is also described here: http://comments.gmane.org/gmane.comp.web.fastcgi.devel/942
+  for (auto signo : {SIGTERM, SIGINT}) {
+    struct sigaction act;
+    sigemptyset(&act.sa_mask);
+    act.sa_flags = 0;
+#ifdef SA_INTERRUPT
+    act.sa_flags |= SA_INTERRUPT;
+#endif
+    act.sa_handler = [](int) { FCGX_ShutdownPending(); };
+    const int result = sigaction(signo, &act, nullptr);
+    if (result != 0) {
+      ATLOG("WARNING: Can't set", signo, "signal handler");
+    }
   }
+
   alohalytics::StatisticsReceiver receiver(argv[1]);
   string gzipped_body;
   long long content_length;