Merge pull request #449 from lionelperrin/master

MVar#take accepts a block as parameter

Author: jdantonio

lib/concurrent/mvar.rb

@@ -78,6 +78,23 @@ def take(timeout = nil)
       end
     end
 
+    # acquires lock on the from an `MVAR`, yields the value to provided block,
+    # and release lock. A timeout can be set to limit the time spent blocked,
+    # in which case it returns `TIMEOUT` if the time is exceeded.
+    # @return [Object] the value returned by the block, or `TIMEOUT`
+    def borrow(timeout = nil)
+      @mutex.synchronize do
+        wait_for_full(timeout)
+
+        # if we timeoud out we'll still be empty
+        if unlocked_full?
+          yield @value
+        else
+          TIMEOUT
+        end
+      end
+    end
+
     # Put a value into an `MVar`, blocking if there is already a value until
     # it is empty. A timeout can be set to limit the time spent blocked, in
     # which case it returns `TIMEOUT` if the time is exceeded.

spec/concurrent/mvar_spec.rb

@@ -70,6 +70,34 @@ def dereferenceable_subject(value, opts = {})
 
     end
 
+    describe '#borrow' do
+
+      it 'yields current value to the block and puts back value' do
+        m = MVar.new(14)
+        expect { |b| m.borrow(&b) }.to yield_with_args(14)
+        expect(m.take).to eq(14)
+      end
+
+      it 'puts back value even if an exception is raised' do
+        m = MVar.new(14)
+        expect { m.borrow { fail 'boom!' } }.to raise_error('boom!')
+        expect(m.take).to eq(14)
+      end
+
+      it 'returns the returned value of the block' do
+        m = MVar.new(14)
+        expect(m.borrow{2}).to eq(2)
+        expect(m.take).to eq(14)
+      end
+
+      it 'returns TIMEOUT on timeout on an empty MVar' do
+        m = MVar.new
+        expect(m.borrow(0.1){}).to eq MVar::TIMEOUT
+      end
+
+    end
+
+
     describe '#put' do
 
       it 'sets the MVar to be empty' do