From 76e034c91336878bc7dc239540ee48a637aec677 Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Sun, 14 Jun 2015 22:03:34 -0600
Subject: [PATCH] protocols: add fire-and-forget RPC

---
 artiq/protocols/fire_and_forget.py | 45 ++++++++++++++++++++++++++++++
 artiq/test/pc_rpc.py               | 14 +++++++++-
 2 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 artiq/protocols/fire_and_forget.py

diff --git a/artiq/protocols/fire_and_forget.py b/artiq/protocols/fire_and_forget.py
new file mode 100644
index 000000000..556774531
--- /dev/null
+++ b/artiq/protocols/fire_and_forget.py
@@ -0,0 +1,45 @@
+import threading
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class FFProxy:
+    """Proxies a target object and runs its methods in the background.
+
+    All method calls to this object are forwarded to the target and executed
+    in a background thread. Method calls return immediately. Exceptions from
+    the target method are turned into warnings. At most one method from the
+    target object may be executed in the background; if a new call is
+    submitted while the previous one is still executing, a warning is printed
+    and the new call is dropped.
+
+    This feature is typically used to wrap slow and non-critical RPCs in
+    experiments.
+    """
+    def __init__(self, target):
+        self.target = target
+        self._thread = None
+
+    def ff_join(self):
+        """Waits until any background method finishes its execution."""
+        if self._thread is not None:
+            self._thread.join()
+
+    def __getattr__(self, k):
+        def run_in_thread(*args, **kwargs):
+            if self._thread is not None and self._thread.is_alive():
+                logger.warning("skipping fire-and-forget call to %r.%s as "
+                               "previous call did not complete",
+                               self.target, k)
+                return
+            def thread_body():
+                try:
+                    getattr(self.target, k)(*args, **kwargs)
+                except:
+                    logger.warning("fire-and-forget call to %r.%s raised an "
+                                   "exception:", self.target, k, exc_info=True)
+            self._thread = threading.Thread(target=thread_body)
+            self._thread.start()
+        return run_in_thread
diff --git a/artiq/test/pc_rpc.py b/artiq/test/pc_rpc.py
index b9e76e19a..1b60d245f 100644
--- a/artiq/test/pc_rpc.py
+++ b/artiq/test/pc_rpc.py
@@ -6,7 +6,7 @@ import time
 
 import numpy as np
 
-from artiq.protocols import pc_rpc
+from artiq.protocols import pc_rpc, fire_and_forget
 
 
 test_address = "::1"
@@ -84,6 +84,18 @@ class RPCCase(unittest.TestCase):
         self._run_server_and_test(self._loop_asyncio_echo)
 
 
+class FireAndForgetCase(unittest.TestCase):
+    def _set_ok(self):
+        self.ok = True
+
+    def test_fire_and_forget(self):
+        self.ok = False
+        p = fire_and_forget.FFProxy(self)
+        p._set_ok()
+        p.ff_join()
+        self.assertTrue(self.ok)
+
+
 class Echo:
     def __init__(self):
         self.terminate_notify = asyncio.Semaphore(0)