[SYCL] Optimize host event wait (#6245)

Author: aelovikov-intel

sycl/source/detail/event_impl.cpp

@@ -50,7 +50,7 @@ event_impl::~event_impl() {
     getPlugin().call<PiApiKind::piEventRelease>(MEvent);
 }
 
-void event_impl::waitInternal() const {
+void event_impl::waitInternal() {
   if (!MHostEvent && MEvent) {
     getPlugin().call<PiApiKind::piEventsWait>(1, &MEvent);
     return;
@@ -61,8 +61,11 @@ void event_impl::waitInternal() const {
         make_error_code(errc::invalid),
         "waitInternal method cannot be used for a discarded event.");
 
-  while (MState != HES_Complete)
-    ;
+  if (MState == HES_Complete)
+    return;
+
+  std::unique_lock lock(MMutex);
+  cv.wait(lock, [this] { return MState == HES_Complete; });
 }
 
 void event_impl::setComplete() {
@@ -77,6 +80,7 @@ void event_impl::setComplete() {
 #else
     MState.store(static_cast<int>(HES_Complete));
 #endif
+    cv.notify_all();
     return;
   }
 
@@ -190,8 +194,7 @@ void event_impl::instrumentationEpilog(void *TelemetryEvent,
 #endif
 }
 
-void event_impl::wait(
-    std::shared_ptr<cl::sycl::detail::event_impl> Self) const {
+void event_impl::wait(std::shared_ptr<cl::sycl::detail::event_impl> Self) {
   if (MState == HES_Discarded)
     throw sycl::exception(make_error_code(errc::invalid),
                           "wait method cannot be used for a discarded event.");

sycl/source/detail/event_impl.hpp

@@ -17,6 +17,7 @@
 
 #include <atomic>
 #include <cassert>
+#include <condition_variable>
 
 __SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
@@ -70,7 +71,7 @@ class event_impl {
   /// Self is needed in order to pass shared_ptr to Scheduler.
   ///
   /// \param Self is a pointer to this event.
-  void wait(std::shared_ptr<cl::sycl::detail::event_impl> Self) const;
+  void wait(std::shared_ptr<cl::sycl::detail::event_impl> Self);
 
   /// Waits for the event.
   ///
@@ -112,7 +113,7 @@ class event_impl {
   ~event_impl();
 
   /// Waits for the event with respect to device type.
-  void waitInternal() const;
+  void waitInternal();
 
   /// Marks this event as completed.
   void setComplete();
@@ -248,6 +249,7 @@ class event_impl {
   bool MNeedsCleanupAfterWait = false;
 
   std::mutex MMutex;
+  std::condition_variable cv;
 };
 
 } // namespace detail