[14_0_X] Introduce edm::Async service, and use it in CUDA and Alpaka modules

FWCore/Concurrency/BuildFile.xml

@@ -1,4 +1,4 @@
-<use name="FWCore/Utilities" source_only="1"/>
+<use name="FWCore/Utilities"/>
 <use name="tbb"/>
 <export>
   <lib name="1"/>

FWCore/Concurrency/interface/Async.h

@@ -0,0 +1,34 @@
+#ifndef FWCore_Concurrency_Async_h
+#define FWCore_Concurrency_Async_h
+
+#include "FWCore/Concurrency/interface/WaitingTaskWithArenaHolder.h"
+#include "FWCore/Concurrency/interface/WaitingThreadPool.h"
+
+namespace edm {
+  // All member functions are thread safe
+  class Async {
+  public:
+    Async() = default;
+    virtual ~Async() noexcept;
+
+    // prevent copying and moving
+    Async(Async const&) = delete;
+    Async(Async&&) = delete;
+    Async& operator=(Async const&) = delete;
+    Async& operator=(Async&&) = delete;
+
+    template <typename F, typename G>
+    void runAsync(WaitingTaskWithArenaHolder holder, F&& func, G&& errorContextFunc) {
+      ensureAllowed();
+      pool_.runAsync(std::move(holder), std::forward<F>(func), std::forward<G>(errorContextFunc));
+    }
+
+  protected:
+    virtual void ensureAllowed() const = 0;
+
+  private:
+    WaitingThreadPool pool_;
+  };
+}  // namespace edm
+
+#endif

FWCore/Concurrency/interface/WaitingThreadPool.h

@@ -0,0 +1,106 @@
+#ifndef FWCore_Concurrency_WaitingThreadPool_h
+#define FWCore_Concurrency_WaitingThreadPool_h
+
+#include "FWCore/Utilities/interface/ConvertException.h"
+#include "FWCore/Utilities/interface/ReusableObjectHolder.h"
+#include "FWCore/Concurrency/interface/WaitingTaskWithArenaHolder.h"
+
+#include <condition_variable>
+#include <mutex>
+#include <thread>
+
+namespace edm {
+  namespace impl {
+    class WaitingThread {
+    public:
+      WaitingThread();
+      ~WaitingThread() noexcept;
+
+      WaitingThread(WaitingThread const&) = delete;
+      WaitingThread& operator=(WaitingThread&&) = delete;
+      WaitingThread(WaitingThread&&) = delete;
+      WaitingThread& operator=(WaitingThread const&) = delete;
+
+      template <typename F, typename G>
+      void run(WaitingTaskWithArenaHolder holder,
+               F&& func,
+               G&& errorContextFunc,
+               std::shared_ptr<WaitingThread> thisPtr) {
+        std::unique_lock lk(mutex_);
+        func_ = [holder = std::move(holder),
+                 func = std::forward<F>(func),
+                 errorContext = std::forward<G>(errorContextFunc)]() mutable {
+          try {
+            convertException::wrap([&func]() { func(); });
+          } catch (cms::Exception& e) {
+            e.addContext(errorContext());
+            holder.doneWaiting(std::current_exception());
+          }
+        };
+        thisPtr_ = std::move(thisPtr);
+        cond_.notify_one();
+      }
+
+    private:
+      void stopThread() {
+        std::unique_lock lk(mutex_);
+        stopThread_ = true;
+        cond_.notify_one();
+      }
+
+      void threadLoop() noexcept;
+
+      std::thread thread_;
+      std::mutex mutex_;
+      std::condition_variable cond_;
+      CMS_THREAD_GUARD(mutex_) std::function<void()> func_;
+      // The purpose of thisPtr_ is to keep the WaitingThread object
+      // outside of the WaitingThreadPool until the func_ has returned.
+      CMS_THREAD_GUARD(mutex_) std::shared_ptr<WaitingThread> thisPtr_;
+      CMS_THREAD_GUARD(mutex_) bool stopThread_ = false;
+    };
+  }  // namespace impl
+
+  // Provides a mechanism to run the function 'func' asynchronously,
+  // i.e. without the calling thread to wait for the func() to return.
+  // The func should do as little work (outside of the TBB threadpool)
+  // as possible. The func must terminate eventually. The intended use
+  // case are blocking synchronization calls with external entities,
+  // where the calling thread is suspended while waiting.
+  //
+  // The func() is run in a thread that belongs to a separate pool of
+  // threads than the calling thread. Remotely similar to
+  // std::async(), but instead of dealing with std::futures, takes an
+  // edm::WaitingTaskWithArenaHolder object, that is signaled upon the
+  // func() returning or throwing an exception.
+  //
+  // The caller is responsible for keeping the WaitingThreadPool
+  // object alive at least as long as all asynchronous calls finish.
+  class WaitingThreadPool {
+  public:
+    WaitingThreadPool() = default;
+    WaitingThreadPool(WaitingThreadPool const&) = delete;
+    WaitingThreadPool& operator=(WaitingThreadPool const&) = delete;
+    WaitingThreadPool(WaitingThreadPool&&) = delete;
+    WaitingThreadPool& operator=(WaitingThreadPool&&) = delete;
+
+    /**
+     * \param holder           WaitingTaskWithArenaHolder object to signal the completion of 'func'
+     * \param func             Function to run in a separate thread
+     * \param errorContextFunc Function returning a string-like object
+     *                         that is added to the context of
+     *                         cms::Exception in case 'func' throws an
+     *                         exception
+     */
+    template <typename F, typename G>
+    void runAsync(WaitingTaskWithArenaHolder holder, F&& func, G&& errorContextFunc) {
+      auto thread = pool_.makeOrGet([]() { return std::make_unique<impl::WaitingThread>(); });
+      thread->run(std::move(holder), std::forward<F>(func), std::forward<G>(errorContextFunc), std::move(thread));
+    }
+
+  private:
+    edm::ReusableObjectHolder<impl::WaitingThread> pool_;
+  };
+}  // namespace edm
+
+#endif

FWCore/Concurrency/src/Async.cc

@@ -0,0 +1,5 @@
+#include "FWCore/Concurrency/interface/Async.h"
+
+namespace edm {
+  Async::~Async() noexcept = default;
+}

FWCore/Concurrency/src/WaitingThreadPool.cc

@@ -0,0 +1,58 @@
+#include "FWCore/Concurrency/interface/WaitingThreadPool.h"
+
+#include <cassert>
+#include <string_view>
+
+#include <pthread.h>
+
+namespace edm::impl {
+  WaitingThread::WaitingThread() {
+    thread_ = std::thread(&WaitingThread::threadLoop, this);
+    static constexpr auto poolName = "edm async pool";
+    // pthread_setname_np() string length is limited to 16 characters,
+    // including the null termination
+    static_assert(std::string_view(poolName).size() < 16);
+
+    int err = pthread_setname_np(thread_.native_handle(), poolName);
+    // According to the glibc documentation, the only error
+    // pthread_setname_np() can return is about the argument C-string
+    // being too long. We already check above the C-string is shorter
+    // than the limit was at the time of writing. In order to capture
+    // if the limit shortens, or other error conditions get added,
+    // let's assert() anyway (exception feels overkill)
+    assert(err == 0);
+  }
+
+  WaitingThread::~WaitingThread() noexcept {
+    // When we are shutting down, we don't care about any possible
+    // system errors anymore
+    CMS_SA_ALLOW try {
+      stopThread();
+      thread_.join();
+    } catch (...) {
+    }
+  }
+
+  void WaitingThread::threadLoop() noexcept {
+    std::unique_lock lk(mutex_);
+
+    while (true) {
+      cond_.wait(lk, [this]() { return static_cast<bool>(func_) or stopThread_; });
+      if (stopThread_) {
+        // There should be no way to stop the thread when it as the
+        // func_ assigned, but let's make sure
+        assert(not thisPtr_);
+        break;
+      }
+      func_();
+      // Must return this WaitingThread to the ReusableObjectHolder in
+      // the WaitingThreadPool before resettting func_ (that holds the
+      // WaitingTaskWithArenaHolder, that enables the progress in the
+      // TBB thread pool) in order to meet the requirement of
+      // ReusableObjectHolder destructor that there are no outstanding
+      // objects.
+      thisPtr_.reset();
+      decltype(func_)().swap(func_);
+    }
+  }
+}  // namespace edm::impl

FWCore/Concurrency/test/test_catch2_Async.cc

@@ -0,0 +1,101 @@
+#include "catch.hpp"
+
+#include <atomic>
+
+#include "oneapi/tbb/global_control.h"
+
+#include "FWCore/Concurrency/interface/chain_first.h"
+#include "FWCore/Concurrency/interface/FinalWaitingTask.h"
+#include "FWCore/Concurrency/interface/Async.h"
+
+namespace {
+  constexpr char const* errorContext() { return "AsyncServiceTest"; }
+
+  class AsyncServiceTest : public edm::Async {
+  public:
+    enum class State { kAllowed, kDisallowed, kShutdown };
+
+    AsyncServiceTest() = default;
+
+    void setAllowed(bool allowed) noexcept { allowed_ = allowed; }
+
+  private:
+    void ensureAllowed() const final {
+      if (not allowed_) {
+        throw std::runtime_error("Calling run in this context is not allowed");
+      }
+    }
+
+    std::atomic<bool> allowed_ = true;
+  };
+}  // namespace
+
+TEST_CASE("Test Async", "[edm::Async") {
+  // Using parallelism 2 here because otherwise the
+  // tbb::task_arena::enqueue() in WaitingTaskWithArenaHolder will
+  // start a new TBB thread that "inherits" the name from the
+  // WaitingThreadPool thread.
+  oneapi::tbb::global_control control(oneapi::tbb::global_control::max_allowed_parallelism, 2);
+
+  SECTION("Normal operation") {
+    AsyncServiceTest service;
+    std::atomic<int> count{0};
+
+    oneapi::tbb::task_group group;
+    edm::FinalWaitingTask waitTask{group};
+
+    {
+      using namespace edm::waiting_task::chain;
+      auto h1 = first([&service, &count](edm::WaitingTaskHolder h) {
+                  edm::WaitingTaskWithArenaHolder h2(std::move(h));
+                  service.runAsync(
+                      h2, [&count]() { ++count; }, errorContext);
+                }) |
+                lastTask(edm::WaitingTaskHolder(group, &waitTask));
+
+      auto h2 = first([&service, &count](edm::WaitingTaskHolder h) {
+                  edm::WaitingTaskWithArenaHolder h2(std::move(h));
+                  service.runAsync(
+                      h2, [&count]() { ++count; }, errorContext);
+                }) |
+                lastTask(edm::WaitingTaskHolder(group, &waitTask));
+      h2.doneWaiting(std::exception_ptr());
+      h1.doneWaiting(std::exception_ptr());
+    }
+    waitTask.waitNoThrow();
+    REQUIRE(count.load() == 2);
+    REQUIRE(waitTask.done());
+    REQUIRE(not waitTask.exceptionPtr());
+  }
+
+  SECTION("Disallowed") {
+    AsyncServiceTest service;
+    std::atomic<int> count{0};
+
+    oneapi::tbb::task_group group;
+    edm::FinalWaitingTask waitTask{group};
+
+    {
+      using namespace edm::waiting_task::chain;
+      auto h = first([&service, &count](edm::WaitingTaskHolder h) {
+                 edm::WaitingTaskWithArenaHolder h2(std::move(h));
+                 service.runAsync(
+                     h2, [&count]() { ++count; }, errorContext);
+                 service.setAllowed(false);
+               }) |
+               then([&service, &count](edm::WaitingTaskHolder h) {
+                 edm::WaitingTaskWithArenaHolder h2(std::move(h));
+                 service.runAsync(
+                     h2, [&count]() { ++count; }, errorContext);
+               }) |
+               lastTask(edm::WaitingTaskHolder(group, &waitTask));
+      h.doneWaiting(std::exception_ptr());
+    }
+    waitTask.waitNoThrow();
+    REQUIRE(count.load() == 1);
+    REQUIRE(waitTask.done());
+    REQUIRE(waitTask.exceptionPtr());
+    REQUIRE_THROWS_WITH(std::rethrow_exception(waitTask.exceptionPtr()),
+                        Catch::Contains("Calling run in this context is not allowed"));
+  }
+}