Merge pull request #1138 from ajbeamon/python-fix-signal-handler

Python now blocks on a future in Python rather than in native code to…

bindings/python/fdb/impl.py

@@ -30,6 +30,7 @@ import datetime
 import platform
 import os
 import sys
+import multiprocessing
 
 from fdb import six
 
@@ -38,6 +39,8 @@ _network_thread_reentrant_lock = threading.RLock()
 
 _open_file = open
 
+_thread_local_storage = threading.local()
+
 import weakref
 
 
@@ -593,7 +596,27 @@ class Future(_FDBBase):
         return bool(self.capi.fdb_future_is_ready(self.fpointer))
 
     def block_until_ready(self):
-        self.capi.fdb_future_block_until_ready(self.fpointer)
+        # Checking readiness is faster than using the callback, so it saves us time if we are already
+        # ready. It also doesn't add much to the cost of this function
+        if not self.is_ready():
+            # Blocking in the native client from the main thread prevents Python from handling signals.
+            # To avoid that behavior, we implement the blocking in Python using semaphores and on_ready.
+            # Using a Semaphore is faster than an Event, and we create only one per thread to avoid the 
+            # cost of creating one every time.
+            semaphore = getattr(_thread_local_storage, 'future_block_semaphore', None)
+            if semaphore is None:
+                semaphore = multiprocessing.Semaphore(0)
+                _thread_local_storage.future_block_semaphore = semaphore
+
+            self.on_ready(lambda self: semaphore.release())
+
+            try:
+                semaphore.acquire()
+            except:
+                # If this semaphore didn't actually get released, then we need to replace our thread-local
+                # copy so that later callers still function correctly
+                _thread_local_storage.future_block_semaphore = multiprocessing.Semaphore(0)
+                raise
 
     def on_ready(self, callback):
         def cb_and_delref(ignore):

documentation/sphinx/source/release-notes.rst

@@ -30,6 +30,7 @@ Bindings
 * Golang: Deprecated ``fdb.StartNetwork``, ``fdb.Open``, ``fdb.MustOpen``, and ``fdb.CreateCluster`` and added ``fdb.OpenDatabase`` and ``fdb.MustOpenDatabase``. The preferred way to start the network and get a ``Database`` is by using ``FDB.OpenDatabase`` or ``FDB.OpenDefault``. `(PR #942) <https://github.com/apple/foundationdb/pull/942>`_
 * Flow: Deprecated ``API::createCluster`` and ``Cluster`` and added ``API::createDatabase``. The preferred way to get a ``Database`` is by using ``API::createDatabase``. `(PR #942) <https://github.com/apple/foundationdb/pull/942>`_
 * Golang: Added ``fdb.Printable`` to print a human-readable string for a given byte array. Add ``Key.String()``, which converts the ``Key`` to a ``string`` using the ``Printable`` function. `(PR #1010) <https://github.com/apple/foundationdb/pull/1010>`_
+* Python: Python signal handling didn't work when waiting on a future. In particular, pressing Ctrl-C would not successfully interrupt the program. `(PR #1138) <https://github.com/apple/foundationdb/pull/1138>`_
 
 Other Changes
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