An IOExecutor that executes under mapped fiber context.

Summary:
This should help executing sync thrift handlers on fibers. This allows the handler methods to achieve concurrency by awaiting.

Test Plan: Chimera unit tests (which also accesses running FacebookBase methods in fiber context!)

Reviewed By: davejwatson@fb.com

Subscribers: trunkagent, hannesr, andrii, folly-diffs@, jsedgwick, haijunz, yfeldblum, alandau, chalfant

FB internal diff: D2015886

Signature: t1:2015886:1430156870:a84499e0e781f5e6e77f48f1f3063f53d0968698

folly/Makefile.am

@@ -83,6 +83,7 @@ nobase_follyinclude_HEADERS = \
 	experimental/fibers/ExecutionObserver.h \
 	experimental/fibers/Fiber.h \
 	experimental/fibers/Fiber-inl.h \
+	experimental/fibers/FiberIOExecutor.h \
 	experimental/fibers/FiberManager.h \
 	experimental/fibers/FiberManager-inl.h \
 	experimental/fibers/FiberManagerMap.h \

folly/experimental/fibers/FiberIOExecutor.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2015 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <folly/experimental/fibers/FiberManagerMap.h>
+#include <folly/wangle/concurrent/IOExecutor.h>
+
+namespace folly { namespace fibers {
+
+/**
+ * @class FiberIOExecutor
+ * @brief An IOExecutor that executes funcs under mapped fiber context
+ *
+ * A FiberIOExecutor wraps an IOExecutor, but executes funcs on the FiberManager
+ * mapped to the underlying IOExector's event base.
+ */
+class FiberIOExecutor : public folly::wangle::IOExecutor {
+ public:
+  explicit FiberIOExecutor(
+      const std::shared_ptr<folly::wangle::IOExecutor>& ioExecutor)
+      : ioExecutor_(ioExecutor) {}
+
+  virtual void add(std::function<void()> f) override {
+    auto eventBase = ioExecutor_->getEventBase();
+    getFiberManager(*eventBase).add(std::move(f));
+  }
+
+  virtual EventBase* getEventBase() override {
+    return ioExecutor_->getEventBase();
+  }
+
+ private:
+  std::shared_ptr<folly::wangle::IOExecutor> ioExecutor_;
+};
+
+}}