Revert r211287, "Remove support for LLVM runtime multi-threading."

libclang still requires it on cygming, lack of incomplete <mutex>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211592 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 20 insertions, 4 deletions

diff --git a/include/llvm/Support/ManagedStatic.h b/include/llvm/Support/ManagedStatic.h
index d8fbfeb8e2..1bb8cea092 100644
--- a/include/llvm/Support/ManagedStatic.h
+++ b/include/llvm/Support/ManagedStatic.h
@@ -103,6 +103,9 @@ void llvm_shutdown();
 /// llvm_shutdown() when it is destroyed.
 struct llvm_shutdown_obj {
   llvm_shutdown_obj() { }
+  explicit llvm_shutdown_obj(bool multithreaded) {
+    if (multithreaded) llvm_start_multithreaded();
+  }
   ~llvm_shutdown_obj() { llvm_shutdown(); }
 };
 
diff --git a/include/llvm/Support/Threading.h b/include/llvm/Support/Threading.h
index 7e8758407c..d84d118679 100644
--- a/include/llvm/Support/Threading.h
+++ b/include/llvm/Support/Threading.h
@@ -7,8 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file declares helper functions for running LLVM in a multi-threaded
-// environment.
+// TThis file defines llvm_start_multithreaded() and friends.
 //
 //===----------------------------------------------------------------------===//
 
@@ -16,8 +15,22 @@
 #define LLVM_SUPPORT_THREADING_H
 
 namespace llvm {
-  /// Returns true if LLVM is compiled with support for multi-threading, and
-  /// false otherwise.
+  /// llvm_start_multithreaded - Allocate and initialize structures needed to
+  /// make LLVM safe for multithreading.  The return value indicates whether
+  /// multithreaded initialization succeeded.  LLVM will still be operational
+  /// on "failed" return, and will still be safe for hosting threading
+  /// applications in the JIT, but will not be safe for concurrent calls to the
+  /// LLVM APIs.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  bool llvm_start_multithreaded();
+
+  /// llvm_stop_multithreaded - Deallocate structures necessary to make LLVM
+  /// safe for multithreading.
+  /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
+  void llvm_stop_multithreaded();
+
+  /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe
+  /// mode or not.
   bool llvm_is_multithreaded();
 
   /// llvm_execute_on_thread - Execute the given \p UserFn on a separate