Re-add the warning for workers terminated due to a signal

Original: b695b49 (benoitc#2475)
Reverted: 76f8da2

The warnings are printed later in the main loop, not directly in the signal
handler. This should fix the RuntimeError from benoitc#2564.

gunicorn/arbiter.py

@@ -64,6 +64,8 @@ def __init__(self, app):
         self.master_pid = 0
         self.master_name = "Master"
 
+        self.signal_warnings = []
+
         cwd = util.getcwd()
 
         args = sys.argv[:]
@@ -204,6 +206,14 @@ def run(self):
             while True:
                 self.maybe_promote_master()
 
+                warnings, self.signal_warnings = self.signal_warnings, []
+                for (wpid, sig) in warnings:
+                    self.log.warning(
+                        "Worker with pid %s was terminated due to signal %s",
+                        wpid,
+                        sig,
+                    )
+
                 sig = self.SIG_QUEUE.pop(0) if self.SIG_QUEUE else None
                 if sig is None:
                     self.sleep()
@@ -526,6 +536,12 @@ def reap_workers(self):
                     if exitcode == self.APP_LOAD_ERROR:
                         reason = "App failed to load."
                         raise HaltServer(reason, self.APP_LOAD_ERROR)
+                    if os.WIFSIGNALED(status):
+                        # Log it later. Not in the SIGCHLD handler. #2564
+                        # https://stackoverflow.com/q/45680378
+                        self.signal_warnings.append(
+                            (wpid, os.WTERMSIG(status))
+                        )
 
                     worker = self.WORKERS.pop(wpid, None)
                     if not worker: