Command throttling breaking HWM algorithms -- fixed.

When HWM was set to small value it may have happened that command
indicating that pipe is ready for writing wasn't processed
because of command throttling.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

2 files changed, 46 insertions, 4 deletions

diff --git a/src/socket_base.cpp b/src/socket_base.cpp
index ad8666a..86c01b0 100644
--- a/src/socket_base.cpp
+++ b/src/socket_base.cpp
@@ -614,11 +614,18 @@ int xs::socket_base_t::send (msg_t *msg_, int flags_)
     if (unlikely (errno != EAGAIN))
         return -1;
 
-    //  In case of non-blocking send we'll simply propagate
-    //  the error - including EAGAIN - up the stack.
     int timeout = sndtimeo ();
-    if (flags_ & XS_DONTWAIT || timeout == 0)
-        return -1;
+    if (flags_ & XS_DONTWAIT || timeout == 0) {
+
+        //  It looks like pipe is full. However, previous process_commands may
+        //  have done nothing because of the throttling. Thus, let's give it
+        //  last try and force commands to be processed. Then try to re-send
+        //  the message.
+        rc = process_commands (0, false);
+        if (unlikely (rc != 0))
+            return -1;
+        return xsend (msg_, flags_);
+    }
 
     //  Compute the time when the timeout should occur.
     //  If the timeout is infite, don't care. 
diff --git a/tests/hwm.cpp b/tests/hwm.cpp
index 93e8910..10afa36 100644
--- a/tests/hwm.cpp
+++ b/tests/hwm.cpp
@@ -77,5 +77,40 @@ int XS_TEST_MAIN ()
     rc = xs_term (ctx);
     assert (rc == 0);
 
+    //  Following part of the tests checks whether small HWMs don't interact
+    //  with command throttling in strange ways.
+
+    ctx = xs_init ();
+    assert (ctx);
+    void *s1 = xs_socket (ctx, XS_PULL);
+    assert (s1);
+    void *s2 = xs_socket (ctx, XS_PUSH);
+    assert (s2);
+
+    hwm = 5;
+    rc = xs_setsockopt (s2, XS_SNDHWM, &hwm, sizeof (hwm));
+    assert (rc == 0);
+
+    rc = xs_bind (s1, "tcp://127.0.0.1:5858");
+    assert (rc >= 0);
+    rc = xs_connect (s2, "tcp://127.0.0.1:5858");
+    assert (rc >= 0);
+
+    for (int i = 0; i < 10; i++)
+    {
+        rc = xs_send (s2, "test", 4, XS_DONTWAIT);
+        assert (rc == 4);
+        char buf [4];
+        rc = xs_recv (s1, buf, sizeof (buf), 0);
+        assert (rc == 4);
+    }
+
+    rc = xs_close (s2);
+    assert (rc == 0);
+    rc = xs_close (s1);
+    assert (rc == 0);
+    rc = xs_term (ctx);
+    assert (rc == 0);
+
 	return 0;
 }