Make request_allowed? thread safe

lib/semian/circuit_breaker.rb

@@ -2,6 +2,8 @@ module Semian
   class CircuitBreaker #:nodoc:
     extend Forwardable
 
+    def_delegators :@state, :closed?, :open?, :half_open?
+
     def initialize(name, exceptions:, success_threshold:, error_threshold:, error_timeout:, implementation:)
       @name = name.to_sym
       @success_count_threshold = success_threshold
@@ -15,6 +17,8 @@ def initialize(name, exceptions:, success_threshold:, error_threshold:, error_ti
     end
 
     def acquire
+      half_open if open? && error_timeout_expired?
+
       raise OpenCircuitError unless request_allowed?
 
       result = nil
@@ -30,9 +34,10 @@ def acquire
     end
 
     def request_allowed?
-      return true if closed?
-      half_open if error_timeout_expired?
-      !open?
+      closed? ||
+        half_open? ||
+        # The circuit breaker is officially open, but it will transition to half-open on the next attempt.
+        (open? && error_timeout_expired?)
     end
 
     def mark_failed(_error)
@@ -64,9 +69,6 @@ def destroy
 
     private
 
-    def_delegators :@state, :closed?, :open?, :half_open?
-    private :closed?, :open?, :half_open?
-
     def close
       log_state_transition(:closed)
       @state.close

lib/semian/protected_resource.rb

@@ -3,7 +3,8 @@ class ProtectedResource
     extend Forwardable
 
     def_delegators :@resource, :destroy, :count, :semid, :tickets, :name
-    def_delegators :@circuit_breaker, :reset, :mark_failed, :mark_success, :request_allowed?
+    def_delegators :@circuit_breaker, :reset, :mark_failed, :mark_success, :request_allowed?,
+                   :open?, :closed?, :half_open?
 
     def initialize(resource, circuit_breaker)
       @resource = resource

lib/semian/unprotected_resource.rb

@@ -30,6 +30,18 @@ def semid
     def reset
     end
 
+    def open?
+      false
+    end
+
+    def closed?
+      true
+    end
+
+    def half_open?
+      false
+    end
+
     def request_allowed?
       true
     end

test/circuit_breaker_test.rb

@@ -86,6 +86,18 @@ def test_sparse_errors_dont_open_circuit
     Semian.destroy(:three)
   end
 
+  def test_request_allowed_query_doesnt_trigger_transitions
+    Timecop.travel(Time.now - 6) do
+      open_circuit!
+
+      refute_predicate @resource, :request_allowed?
+      assert_predicate @resource, :open?
+    end
+
+    assert_predicate @resource, :request_allowed?
+    assert_predicate @resource, :open?
+  end
+
   private
 
   def open_circuit!(resource = @resource)