Remove last use of tbb::task::suspend

The defered task implementation avoids the problems where suspend
could resume a function on a different thread.

FWCore/Concurrency/interface/include_first_syncWait.h

@@ -8,32 +8,19 @@
 //  Created by Chris Jones on 2/24/21.
 //
 #include "FWCore/Concurrency/interface/WaitingTaskHolder.h"
+#include "FWCore/Concurrency/interface/FinalWaitingTask.h"
 #include "oneapi/tbb/task_group.h"
-#include "oneapi/tbb/task.h"
 #include <exception>
 
 namespace edm {
   template <typename F>
   [[nodiscard]] std::exception_ptr syncWait(F&& iFunc) {
     std::exception_ptr exceptPtr{};
-    //oneapi::tbb::task::suspend can only be run from within a task running in this arena. For 1 thread,
-    // it is often (always?) the case where not such task is being run here. Therefore we need
-    // to use a temp task_group to start up such a task.
     oneapi::tbb::task_group group;
-    group.run([&]() {
-      oneapi::tbb::task::suspend([&](oneapi::tbb::task::suspend_point tag) {
-        auto waitTask = make_waiting_task([tag, &exceptPtr](std::exception_ptr const* iExcept) {
-          if (iExcept) {
-            exceptPtr = *iExcept;
-          }
-          oneapi::tbb::task::resume(tag);
-        });
-        iFunc(WaitingTaskHolder(group, waitTask));
-      });  //suspend
-    });    //group.run
+    FinalWaitingTask last{group};
+    group.run([&]() { iFunc(WaitingTaskHolder(group, &last)); });  //group.run
 
-    group.wait();
-    return exceptPtr;
+    return last.waitNoThrow();
   }
 }  // namespace edm
 #endif /* FWCore_Concurrency_syncWait_h */

FWCore/Concurrency/src/SerialTaskQueue.cc

@@ -12,7 +12,7 @@
 //
 
 // system include files
-#include "oneapi/tbb/task.h"
+#include "oneapi/tbb/task_group.h"
 
 // user include files
 #include "FWCore/Concurrency/interface/SerialTaskQueue.h"
@@ -30,11 +30,8 @@ SerialTaskQueue::~SerialTaskQueue() {
   bool isTaskChosen = m_taskChosen;
   if ((not isEmpty and not isPaused()) or isTaskChosen) {
     oneapi::tbb::task_group g;
-    g.run([&g, this]() {
-      oneapi::tbb::task::suspend([&g, this](oneapi::tbb::task::suspend_point tag) {
-        push(g, [tag]() { oneapi::tbb::task::resume(tag); });
-      });  //suspend
-    });    //group run
+    tbb::task_handle last{g.defer([]() {})};
+    push(g, [&g, &last]() { g.run(std::move(last)); });
     g.wait();
   }
 }