Fixes issue #9535: Fix pending signals that have been received but not

yet handled by Python to not persist after os.fork() in the child process.

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.4.0 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #9535: Fix pending signals that have been received but not yet
+  handled by Python to not persist after os.fork() in the child process.
+
 - Issue #14794: Fix slice.indices to return correct results for huge values,
   rather than raising OverflowError.
 

Modules/signalmodule.c

@@ -1389,9 +1389,25 @@ PyOS_InterruptOccurred(void)
     return 0;
 }
 
+static void
+_clear_pending_signals(void)
+{
+    int i;
+    if (!is_tripped)
+        return;
+    is_tripped = 0;
+    for (i = 1; i < NSIG; ++i) {
+        Handlers[i].tripped = 0;
+    }
+}
+
 void
 PyOS_AfterFork(void)
 {
+    /* Clear the signal flags after forking so that they aren't handled
+     * in both processes if they came in just before the fork() but before
+     * the interpreter had an opportunity to call the handlers.  issue9535. */
+    _clear_pending_signals();
 #ifdef WITH_THREAD
     /* PyThread_ReInitTLS() must be called early, to make sure that the TLS API
      * can be called safely. */