vendor/llvm-project/llvmorg-10-init-17466-ge26a78e7085

1 files changed, 64 insertions, 18 deletions

diff --git a/llvm/lib/Support/Parallel.cpp b/llvm/lib/Support/Parallel.cpp
index 355c64b7d0793..523665d14b029 100644
--- a/llvm/lib/Support/Parallel.cpp
+++ b/llvm/lib/Support/Parallel.cpp
@@ -8,14 +8,17 @@
 
 #include "llvm/Support/Parallel.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/ManagedStatic.h"
 
 #if LLVM_ENABLE_THREADS
 
 #include "llvm/Support/Threading.h"
 
 #include <atomic>
+#include <future>
 #include <stack>
 #include <thread>
+#include <vector>
 
 namespace llvm {
 namespace parallel {
@@ -36,30 +39,53 @@ public:
 ///   in filo order.
 class ThreadPoolExecutor : public Executor {
 public:
-  explicit ThreadPoolExecutor(unsigned ThreadCount = hardware_concurrency())
-      : Done(ThreadCount) {
+  explicit ThreadPoolExecutor(unsigned ThreadCount = hardware_concurrency()) {
     // Spawn all but one of the threads in another thread as spawning threads
     // can take a while.
-    std::thread([&, ThreadCount] {
-      for (size_t i = 1; i < ThreadCount; ++i) {
-        std::thread([=] { work(); }).detach();
+    Threads.reserve(ThreadCount);
+    Threads.resize(1);
+    std::lock_guard<std::mutex> Lock(Mutex);
+    Threads[0] = std::thread([&, ThreadCount] {
+      for (unsigned i = 1; i < ThreadCount; ++i) {
+        Threads.emplace_back([=] { work(); });
+        if (Stop)
+          break;
       }
+      ThreadsCreated.set_value();
       work();
-    }).detach();
+    });
   }
 
-  ~ThreadPoolExecutor() override {
-    std::unique_lock<std::mutex> Lock(Mutex);
-    Stop = true;
-    Lock.unlock();
+  void stop() {
+    {
+      std::lock_guard<std::mutex> Lock(Mutex);
+      if (Stop)
+        return;
+      Stop = true;
+    }
     Cond.notify_all();
-    // Wait for ~Latch.
+    ThreadsCreated.get_future().wait();
   }
 
+  ~ThreadPoolExecutor() override {
+    stop();
+    std::thread::id CurrentThreadId = std::this_thread::get_id();
+    for (std::thread &T : Threads)
+      if (T.get_id() == CurrentThreadId)
+        T.detach();
+      else
+        T.join();
+  }
+
+  struct Deleter {
+    static void call(void *Ptr) { ((ThreadPoolExecutor *)Ptr)->stop(); }
+  };
+
   void add(std::function<void()> F) override {
-    std::unique_lock<std::mutex> Lock(Mutex);
-    WorkStack.push(F);
-    Lock.unlock();
+    {
+      std::lock_guard<std::mutex> Lock(Mutex);
+      WorkStack.push(F);
+    }
     Cond.notify_one();
   }
 
@@ -75,19 +101,39 @@ private:
       Lock.unlock();
       Task();
     }
-    Done.dec();
   }
 
   std::atomic<bool> Stop{false};
   std::stack<std::function<void()>> WorkStack;
   std::mutex Mutex;
   std::condition_variable Cond;
-  parallel::detail::Latch Done;
+  std::promise<void> ThreadsCreated;
+  std::vector<std::thread> Threads;
 };
 
 Executor *Executor::getDefaultExecutor() {
-  static ThreadPoolExecutor exec;
-  return &exec;
+  // The ManagedStatic enables the ThreadPoolExecutor to be stopped via
+  // llvm_shutdown() which allows a "clean" fast exit, e.g. via _exit(). This
+  // stops the thread pool and waits for any worker thread creation to complete
+  // but does not wait for the threads to finish. The wait for worker thread
+  // creation to complete is important as it prevents intermittent crashes on
+  // Windows due to a race condition between thread creation and process exit.
+  //
+  // The ThreadPoolExecutor will only be destroyed when the static unique_ptr to
+  // it is destroyed, i.e. in a normal full exit. The ThreadPoolExecutor
+  // destructor ensures it has been stopped and waits for worker threads to
+  // finish. The wait is important as it prevents intermittent crashes on
+  // Windows when the process is doing a full exit.
+  //
+  // The Windows crashes appear to only occur with the MSVC static runtimes and
+  // are more frequent with the debug static runtime.
+  //
+  // This also prevents intermittent deadlocks on exit with the MinGW runtime.
+  static ManagedStatic<ThreadPoolExecutor, object_creator<ThreadPoolExecutor>,
+                       ThreadPoolExecutor::Deleter>
+      ManagedExec;
+  static std::unique_ptr<ThreadPoolExecutor> Exec(&(*ManagedExec));
+  return Exec.get();
 }
 } // namespace