Revert "Remove support for runtime multi-threading."

This reverts revision r210600.

llvm-svn: 210603

1 files changed, 36 insertions, 5 deletions

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index c9f0f2c2e5a..1acfa79b11d 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -19,19 +19,50 @@
 
 using namespace llvm;
 
-llvm::recursive_mutex& llvm::llvm_get_global_lock() {
-  static llvm::recursive_mutex global_lock;
-  return global_lock;
-}
+static bool multithreaded_mode = false;
 
-bool llvm::llvm_is_multithreaded() {
+static sys::Mutex* global_lock = nullptr;
+
+bool llvm::llvm_start_multithreaded() {
 #if LLVM_ENABLE_THREADS != 0
+  assert(!multithreaded_mode && "Already multithreaded!");
+  multithreaded_mode = true;
+  global_lock = new sys::Mutex(true);
+
+  // We fence here to ensure that all initialization is complete BEFORE we
+  // return from llvm_start_multithreaded().
+  sys::MemoryFence();
   return true;
 #else
   return false;
 #endif
 }
 
+void llvm::llvm_stop_multithreaded() {
+#if LLVM_ENABLE_THREADS != 0
+  assert(multithreaded_mode && "Not currently multithreaded!");
+
+  // We fence here to insure that all threaded operations are complete BEFORE we
+  // return from llvm_stop_multithreaded().
+  sys::MemoryFence();
+
+  multithreaded_mode = false;
+  delete global_lock;
+#endif
+}
+
+bool llvm::llvm_is_multithreaded() {
+  return multithreaded_mode;
+}
+
+void llvm::llvm_acquire_global_lock() {
+  if (multithreaded_mode) global_lock->acquire();
+}
+
+void llvm::llvm_release_global_lock() {
+  if (multithreaded_mode) global_lock->release();
+}
+
 #if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
 #include <pthread.h>