Allow custom preLoop and postLoop hooks

Summary:
Hyperclient polls EventBases directly, and it would like to receive the number of events processed per loopPoll() call. The easiest way is to use eb_loop_poll_hook. However this doesn't work for us (see D93285393), because these hooks are per-process, only 1 hook is allowed. ucache already uses these hooks, and hyperclient will be in the same process with ucache, this breaks other tests (see T256167952).
As a result, we would like to have per-EventBase custom preLoop and postLoop hooks.

Reviewed By: spikeh

Differential Revision: D93625126

fbshipit-source-id: 285d3bc9470b51dbcae8e37fa098dae8095565d8

Author: Yikang Xu

third-party/folly/src/folly/io/async/EpollBackend.cpp

@@ -229,6 +229,9 @@ int EpollBackend::eb_event_base_loop(int flags) {
     if (eb_poll_loop_pre_hook) {
       eb_poll_loop_pre_hook(&call_time);
     }
+    if (pollLoopHook_.preLoopHook) {
+      pollLoopHook_.preLoopHook(pollLoopHook_.hookCtx);
+    }
 
     int numEvents;
     do {
@@ -239,6 +242,9 @@ int EpollBackend::eb_event_base_loop(int flags) {
     if (eb_poll_loop_post_hook) {
       eb_poll_loop_post_hook(call_time, numEvents);
     }
+    if (pollLoopHook_.postLoopHook) {
+      pollLoopHook_.postLoopHook(pollLoopHook_.hookCtx, numEvents);
+    }
 
     if (numEvents < 0) {
       return -1;

third-party/folly/src/folly/io/async/EventBaseBackendBase.h

@@ -114,6 +114,23 @@ class EventBaseBackendBase {
       std::function<std::unique_ptr<folly::EventBaseBackendBase>()>;
   using RecvZcCallback = folly::Function<void(ssize_t)>;
 
+  // Per-EventBase hooks invoked around the poll syscall (epoll_wait /
+  // io_uring CQE reaping).  Only EpollBackend and IoUringBackend invoke
+  // these hooks; other backends (e.g. LibeventBackend) do not.
+  //
+  // prePollLoopHook is called immediately before the poll syscall.
+  // postPollLoopHook is called immediately after, receiving the number of
+  // events returned by the syscall.
+  // Both hooks share a single opaque context pointer.
+  using PrePollLoopHook = void (*)(void* ctx);
+  using PostPollLoopHook = void (*)(void* ctx, int numEvents);
+
+  struct PollLoopHook {
+    PrePollLoopHook preLoopHook = nullptr;
+    PostPollLoopHook postLoopHook = nullptr;
+    void* hookCtx = nullptr;
+  };
+
   EventBaseBackendBase() = default;
   virtual ~EventBaseBackendBase() = default;
 
@@ -129,6 +146,10 @@ class EventBaseBackendBase {
       unsigned long /*nbytes*/,
       RecvZcCallback&& /*callback*/) {}
 
+  void setPollLoopHook(PollLoopHook pollLoopHook) {
+    pollLoopHook_ = pollLoopHook;
+  }
+
   virtual event_base* getEventBase() = 0;
   virtual int eb_event_base_loop(int flags) = 0;
   virtual int eb_event_base_loopbreak() = 0;
@@ -139,6 +160,9 @@ class EventBaseBackendBase {
   virtual bool eb_event_active(Event& event, int res) = 0;
 
   virtual bool setEdgeTriggered(Event& /* event */) { return false; }
+
+ protected:
+  PollLoopHook pollLoopHook_;
 };
 
 } // namespace folly

third-party/folly/src/folly/io/async/IoUringBackend.cpp

@@ -1183,13 +1183,20 @@ int IoUringBackend::eb_event_base_loop(int flags) {
     if (eb_poll_loop_pre_hook) {
       eb_poll_loop_pre_hook(&call_time);
     }
+    if (pollLoopHook_.preLoopHook) {
+      pollLoopHook_.preLoopHook(pollLoopHook_.hookCtx);
+    }
 
     // do not wait for events if EVLOOP_NONBLOCK is set
     size_t processedEvents = getActiveEvents(waitForEvents);
 
     if (eb_poll_loop_post_hook) {
       eb_poll_loop_post_hook(call_time, static_cast<int>(processedEvents));
     }
+    if (pollLoopHook_.postLoopHook) {
+      pollLoopHook_.postLoopHook(
+          pollLoopHook_.hookCtx, static_cast<int>(processedEvents));
+    }
 
     size_t numProcessedTimers = 0;