Instrument EventHandlers' execution

Summary:
Add the option to instrument every EventHandler that runs in a
EventBase.

Test Plan:
Unit tests

Reviewed By: davejwatson@fb.com

Subscribers: alikhtarov, folly-diffs@, yfeldblum, chalfant

FB internal diff: D2044546

Tasks: 6958000

Signature: t1:2044546:1432221358:6500d6c1a6631d7a06a18e874d051f2ff3108e10

folly/Makefile.am

@@ -71,6 +71,7 @@ nobase_follyinclude_HEADERS = \
 	EvictingCacheMap.h \
 	experimental/AutoTimer.h \
 	experimental/Bits.h \
+	experimental/ExecutionObserver.h \
 	experimental/EliasFanoCoding.h \
 	experimental/EventCount.h \
 	experimental/fibers/AddTasks.h \
@@ -80,7 +81,6 @@ nobase_follyinclude_HEADERS = \
 	experimental/fibers/BoostContextCompatibility.h \
 	experimental/fibers/EventBaseLoopController.h \
 	experimental/fibers/EventBaseLoopController-inl.h \
-	experimental/fibers/ExecutionObserver.h \
 	experimental/fibers/Fiber.h \
 	experimental/fibers/Fiber-inl.h \
 	experimental/fibers/FiberManager.h \

folly/experimental/fibers/ExecutionObserver.h → folly/experimental/ExecutionObserver.h

@@ -17,7 +17,7 @@
 
 #include <cstdint>
 
-namespace folly { namespace fibers {
+namespace folly {
 
 /**
  * Observes the execution of a task.
@@ -29,23 +29,23 @@ class ExecutionObserver {
   /**
    * Called when a task is about to start executing.
    *
-   * @param id Unique id for the fiber which is starting.
+   * @param id Unique id for the task which is starting.
    */
   virtual void starting(uintptr_t id) noexcept = 0;
 
   /**
    * Called when a task is ready to run.
    *
-   * @param id Unique id for the fiber which is ready to run.
+   * @param id Unique id for the task which is ready to run.
    */
   virtual void runnable(uintptr_t id) noexcept = 0;
 
   /**
    * Called just after a task stops executing.
    *
-   * @param id Unique id for the fiber which is stopping.
+   * @param id Unique id for the task which stopped.
    */
   virtual void stopped(uintptr_t id) noexcept = 0;
 };
 
-}} // namespace folly::fibers
+} // namespace folly

folly/experimental/fibers/FiberManager.h

@@ -29,8 +29,8 @@
 #include <folly/IntrusiveList.h>
 #include <folly/futures/Try.h>
 
+#include <folly/experimental/ExecutionObserver.h>
 #include <folly/experimental/fibers/BoostContextCompatibility.h>
-#include <folly/experimental/fibers/ExecutionObserver.h>
 #include <folly/experimental/fibers/Fiber.h>
 #include <folly/experimental/fibers/traits.h>
 

folly/io/async/EventBase.cpp

@@ -155,7 +155,8 @@ EventBase::EventBase(bool enableTimeMeasurement)
   , latestLoopCnt_(nextLoopCnt_)
   , startWork_(0)
   , observer_(nullptr)
-  , observerSampleCount_(0) {
+  , observerSampleCount_(0)
+  , executionObserver_(nullptr) {
   {
     std::lock_guard<std::mutex> lock(libevent_mutex_);
 
@@ -193,7 +194,8 @@ EventBase::EventBase(event_base* evb, bool enableTimeMeasurement)
   , latestLoopCnt_(nextLoopCnt_)
   , startWork_(0)
   , observer_(nullptr)
-  , observerSampleCount_(0) {
+  , observerSampleCount_(0)
+  , executionObserver_(nullptr) {
   if (UNLIKELY(evb_ == nullptr)) {
     LOG(ERROR) << "EventBase(): Pass nullptr as event base.";
     throw std::invalid_argument("EventBase(): event base cannot be nullptr");

folly/io/async/EventBase.h

@@ -21,6 +21,7 @@
 #include <folly/io/async/TimeoutManager.h>
 #include <folly/io/async/Request.h>
 #include <folly/Executor.h>
+#include <folly/experimental/ExecutionObserver.h>
 #include <folly/futures/DrivableExecutor.h>
 #include <memory>
 #include <stack>
@@ -545,6 +546,23 @@ bool runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn);
     return observer_;
   }
 
+  /**
+   * Setup execution observation/instrumentation for every EventHandler
+   * executed in this EventBase.
+   *
+   * @param executionObserver   EventHandle's execution observer.
+   */
+  void setExecutionObserver(ExecutionObserver* observer) {
+    executionObserver_ = observer;
+  }
+
+  /**
+   * Gets the execution observer associated with this EventBase.
+   */
+  ExecutionObserver* getExecutionObserver() {
+    return executionObserver_;
+  }
+
   /**
    * Set the name of the thread that runs this event base.
    */
@@ -702,6 +720,9 @@ bool runImmediatelyOrRunInEventBaseThreadAndWait(const Cob& fn);
   std::shared_ptr<EventBaseObserver> observer_;
   uint32_t observerSampleCount_;
 
+  // EventHandler's execution observer.
+  ExecutionObserver* executionObserver_;
+
   // Name of the thread running this EventBase
   std::string name_;
 };

folly/io/async/EventHandler.cpp

@@ -147,10 +147,19 @@ void EventHandler::libeventCallback(int fd, short events, void* arg) {
   EventHandler* handler = reinterpret_cast<EventHandler*>(arg);
   assert(fd == handler->event_.ev_fd);
 
+  auto observer = handler->eventBase_->getExecutionObserver();
+  if (observer) {
+    observer->starting(reinterpret_cast<uintptr_t>(handler));
+  }
+
   // this can't possibly fire if handler->eventBase_ is nullptr
   (void) handler->eventBase_->bumpHandlingTime();
 
   handler->handlerReady(events);
+
+  if (observer) {
+    observer->stopped(reinterpret_cast<uintptr_t>(handler));
+  }
 }
 
 void EventHandler::setEventBase(EventBase* eventBase) {