RUBY-320: Cassandra::Future.all([]).join hangs forever

Author: stamhankar999

CHANGELOG.md

@@ -1,6 +1,7 @@
 # master
 Bug Fixes:
 * [RUBY-319](https://datastax-oss.atlassian.net/browse/RUBY-319) Support reading decimals in scientific notation with positive exponent.
+* [RUBY-320](https://datastax-oss.atlassian.net/browse/RUBY-320) Cassandra::Future.all([]).join hangs forever
 
 # 3.2.1
 

lib/cassandra/future.rb

@@ -204,7 +204,13 @@ def promise
       end
 
       def all(*futures)
-        futures   = Array(futures.first) if futures.one?
+        # May get called with varargs or an array of futures. In the latter case,
+        # the first element in futures is the array of futures. Promote it.
+        futures = Array(futures.first) if futures.one?
+
+        # Special case where there are no futures to aggregate.
+        return Value.new([]) if futures.empty?
+
         monitor   = Monitor.new
         promise   = Promise.new(@executor)
         remaining = futures.length

spec/cassandra/future_spec.rb

@@ -69,6 +69,11 @@ module Listeners
         futures << Future.error(RuntimeError.new("something happened"))
         expect { Future.all(futures).get }.to raise_error("something happened")
       end
+
+      it 'trivially succeeds when there are no futures' do
+        expect(Future.all.get).to eq([])
+        expect(Future.all([]).get).to eq([])
+      end
     end
 
     describe('#get') do