[PATCH] D61115: Parallel: only allow the first TaskGroup to run tasks parallelly
Fangrui Song via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 25 04:32:45 PDT 2019
This revision was automatically updated to reflect the committed changes.
Closed by commit rL359182: Parallel: only allow the first TaskGroup to run tasks parallelly (authored by MaskRay, committed by ).
Repository:
rL LLVM
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D61115/new/
https://reviews.llvm.org/D61115
Files:
llvm/trunk/include/llvm/Support/Parallel.h
llvm/trunk/lib/Support/Parallel.cpp
Index: llvm/trunk/lib/Support/Parallel.cpp
===================================================================
--- llvm/trunk/lib/Support/Parallel.cpp
+++ llvm/trunk/lib/Support/Parallel.cpp
@@ -17,7 +17,9 @@
#include <stack>
#include <thread>
-using namespace llvm;
+namespace llvm {
+namespace parallel {
+namespace detail {
namespace {
@@ -118,11 +120,28 @@
#endif
}
-void parallel::detail::TaskGroup::spawn(std::function<void()> F) {
- L.inc();
- Executor::getDefaultExecutor()->add([&, F] {
+static std::atomic<int> TaskGroupInstances;
+
+// Latch::sync() called by the dtor may cause one thread to block. If is a dead
+// lock if all threads in the default executor are blocked. To prevent the dead
+// lock, only allow the first TaskGroup to run tasks parallelly. In the scenario
+// of nested parallel_for_each(), only the outermost one runs parallelly.
+TaskGroup::TaskGroup() : Parallel(TaskGroupInstances++ == 0) {}
+TaskGroup::~TaskGroup() { --TaskGroupInstances; }
+
+void TaskGroup::spawn(std::function<void()> F) {
+ if (Parallel) {
+ L.inc();
+ Executor::getDefaultExecutor()->add([&, F] {
+ F();
+ L.dec();
+ });
+ } else {
F();
- L.dec();
- });
+ }
}
+
+} // namespace detail
+} // namespace parallel
+} // namespace llvm
#endif // LLVM_ENABLE_THREADS
Index: llvm/trunk/include/llvm/Support/Parallel.h
===================================================================
--- llvm/trunk/include/llvm/Support/Parallel.h
+++ llvm/trunk/include/llvm/Support/Parallel.h
@@ -73,8 +73,12 @@
class TaskGroup {
Latch L;
+ bool Parallel;
public:
+ TaskGroup();
+ ~TaskGroup();
+
void spawn(std::function<void()> f);
void sync() const { L.sync(); }
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