TVar: Concurrent.leave_transaction, used to fix isolation specs but useful on its own.

Author: chrisseaton

lib/concurrent/tvar.rb

@@ -115,6 +115,9 @@ def atomically
           rescue Transaction::AbortError => e
             transaction.abort
             result = Transaction::ABORTED
+          rescue Transaction::LeaveError => e
+            transaction.abort
+            break result
           rescue => e
             transaction.abort
             raise e
@@ -144,6 +147,11 @@ def abort_transaction
     raise Transaction::AbortError.new
   end
 
+  # Leave a transaction without commiting or aborting - see `Concurrent::atomically`.
+  def leave_transaction
+    raise Transaction::LeaveError.new
+  end
+
   module_function :atomically, :abort_transaction
 
   private
@@ -155,6 +163,7 @@ class Transaction
     ReadLogEntry = Struct.new(:tvar, :version)
 
     AbortError = Class.new(StandardError)
+    LeaveError = Class.new(StandardError)
 
     def initialize
       @read_log  = []

spec/concurrent/tvar_spec.rb

@@ -117,13 +117,15 @@ module Concurrent
           t.value = 1
           a.count_down
           b.wait
+          Concurrent.leave_transaction
         end
       end
 
       Concurrent::atomically do
         a.wait
         expect(t.value).to eq 0
         b.count_down
+        Concurrent.leave_transaction
       end
     end
 
@@ -191,4 +193,24 @@ module Concurrent
 
   end
 
+  describe '#leave_transaction' do
+
+    it 'raises an exception outside an #atomically block' do
+      expect { Concurrent::leave_transaction }.to raise_error(Concurrent::Transaction::LeaveError)
+    end
+
+    it 'neither commits nor aborts a transaction' do
+      t = TVar.new(0)
+
+      Concurrent::atomically do
+        expect(t.value).to eq 0
+        t.value = 14
+        Concurrent::leave_transaction
+      end
+
+      expect(t.value).to eq 0
+    end
+
+  end
+
 end