Issue #1677: Handle better a race condition between the interactive interpreter and

the Ctrl-C signal handler on Windows

Parser/myreadline.c

@@ -40,6 +40,7 @@ static int
 my_fgets(char *buf, int len, FILE *fp)
 {
     char *p;
+    int i;
     while (1) {
         if (PyOS_InputHook != NULL)
             (void)(PyOS_InputHook)();
@@ -49,32 +50,24 @@ my_fgets(char *buf, int len, FILE *fp)
         if (p != NULL)
             return 0; /* No error */
 #ifdef MS_WINDOWS
-        /* In the case of a Ctrl+C or some other external event
-           interrupting the operation:
-           Win2k/NT: ERROR_OPERATION_ABORTED is the most recent Win32
-           error code (and feof() returns TRUE).
-           Win9x: Ctrl+C seems to have no effect on fgets() returning
-           early - the signal handler is called, but the fgets()
-           only returns "normally" (ie, when Enter hit or feof())
+        /* Ctrl-C anywhere on the line or Ctrl-Z if the only character
+           on a line will set ERROR_OPERATION_ABORTED. Under normal
+           circumstances Ctrl-C will also have caused the SIGINT handler
+           to fire. This signal fires in another thread and is not
+           guaranteed to have occurred before this point in the code.
+
+           Therefore: check in a small loop to see if the trigger has
+           fired, in which case assume this is a Ctrl-C event. If it
+           hasn't fired within 10ms assume that this is a Ctrl-Z on its
+           own or that the signal isn't going to fire for some other
+           reason and drop through to check for EOF.
         */
         if (GetLastError()==ERROR_OPERATION_ABORTED) {
-            /* Signals come asynchronously, so we sleep a brief
-               moment before checking if the handler has been
-               triggered (we cant just return 1 before the
-               signal handler has been called, as the later
-               signal may be treated as a separate interrupt).
-            */
-            Sleep(1);
-            if (PyOS_InterruptOccurred()) {
-                return 1; /* Interrupt */
+            for (i = 0; i < 10; i++) {
+                if (PyOS_InterruptOccurred())
+                    return 1;
+                Sleep(1);
             }
-            /* Either the sleep wasn't long enough (need a
-               short loop retrying?) or not interrupted at all
-               (in which case we should revisit the whole thing!)
-               Logging some warning would be nice.  assert is not
-               viable as under the debugger, the various dialogs
-               mean the condition is not true.
-            */
         }
 #endif /* MS_WINDOWS */
         if (feof(fp)) {