diff -r 000000000000 -r 6474c204b198 ipc/ipdl/test/cxx/TestRacyInterruptReplies.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/ipdl/test/cxx/TestRacyInterruptReplies.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,119 @@
+#include "TestRacyInterruptReplies.h"
+
+#include "IPDLUnitTests.h"      // fail etc.
+
+namespace mozilla {
+namespace _ipdltest {
+
+//-----------------------------------------------------------------------------
+// parent
+
+TestRacyInterruptRepliesParent::TestRacyInterruptRepliesParent() : mReplyNum(0)
+{
+    MOZ_COUNT_CTOR(TestRacyInterruptRepliesParent);
+}
+
+TestRacyInterruptRepliesParent::~TestRacyInterruptRepliesParent()
+{
+    MOZ_COUNT_DTOR(TestRacyInterruptRepliesParent);
+}
+
+void
+TestRacyInterruptRepliesParent::Main()
+{
+    int replyNum = -1;
+    if (!CallR_(&replyNum))
+        fail("calling R()");
+
+    if (1 != replyNum)
+        fail("this should have been the first reply to R()");
+
+    if (!SendChildTest())
+        fail("sending ChildStart");
+}
+
+bool
+TestRacyInterruptRepliesParent::RecvA_()
+{
+    int replyNum = -1;
+    // this R() call races with the reply being generated by the other
+    // side to the R() call from Main().  This is a pretty nasty edge
+    // case for which one could argue we're breaking in-order message
+    // delivery, since this side will process the second reply to R()
+    // before the first.
+    if (!CallR_(&replyNum))
+        fail("calling R()");
+
+    if (2 != replyNum)
+        fail("this should have been the second reply to R()");
+
+    return true;
+}
+
+bool
+TestRacyInterruptRepliesParent::Answer_R(int* replyNum)
+{
+    *replyNum = ++mReplyNum;
+
+    if (1 == *replyNum)
+        if (!Send_A())
+            fail("sending _A()");
+
+    return true;
+}
+
+//-----------------------------------------------------------------------------
+// child
+
+TestRacyInterruptRepliesChild::TestRacyInterruptRepliesChild() : mReplyNum(0)
+{
+    MOZ_COUNT_CTOR(TestRacyInterruptRepliesChild);
+}
+
+TestRacyInterruptRepliesChild::~TestRacyInterruptRepliesChild()
+{
+    MOZ_COUNT_DTOR(TestRacyInterruptRepliesChild);
+}
+
+bool
+TestRacyInterruptRepliesChild::AnswerR_(int* replyNum)
+{
+    *replyNum = ++mReplyNum;
+
+    if (1 == *replyNum)
+        SendA_();
+
+    return true;
+}
+
+bool
+TestRacyInterruptRepliesChild::RecvChildTest()
+{
+    int replyNum = -1;
+    if (!Call_R(&replyNum))
+        fail("calling R()");
+
+    if (1 != replyNum)
+        fail("this should have been the first reply to R()");
+
+    Close();
+
+    return true;
+}
+
+bool
+TestRacyInterruptRepliesChild::Recv_A()
+{
+    int replyNum = -1;
+
+    if (!Call_R(&replyNum))
+        fail("calling _R()");
+
+    if (2 != replyNum)
+        fail("this should have been the second reply to R()");
+
+    return true;
+}
+
+} // namespace _ipdltest
+} // namespace mozilla