System: Add llvm_execute_on_thread, which does what it says.

- Primarily useful for running some code with a specified stack size, when
   pthreads are available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118222 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/System/Threading.h

@@ -40,6 +40,20 @@ namespace llvm {
   /// release_global_lock - Release the global lock.  This is a no-op if called
   /// before llvm_start_multithreaded().
   void llvm_release_global_lock();
+
+  /// llvm_execute_on_thread - Execute the given \arg UserFn on a separate
+  /// thread, passing it the provided \arg UserData.
+  ///
+  /// This function does not guarantee that the code will actually be executed
+  /// on a separate thread or honoring the requested stack size, but tries to do
+  /// so where system support is available.
+  ///
+  /// \param UserFn - The callback to execute.
+  /// \param UserData - An argument to pass to the callback function.
+  /// \param RequestedStackSize - If non-zero, a requested size (in bytes) for
+  /// the thread stack.
+  void llvm_execute_on_thread(void (*UserFn)(void*), void *UserData,
+                              unsigned RequestedStackSize = 0);
 }
 
 #endif

lib/System/Threading.cpp

@@ -62,3 +62,55 @@ void llvm::llvm_acquire_global_lock() {
 void llvm::llvm_release_global_lock() {
   if (multithreaded_mode) global_lock->release();
 }
+
+#if defined(LLVM_MULTITHREADED) && defined(HAVE_PTHREAD_H)
+#include <pthread.h>
+
+struct ThreadInfo {
+  void (*UserFn)(void *);
+  void *UserData;
+};
+static void *ExecuteOnThread_Dispatch(void *Arg) {
+  ThreadInfo *TI = reinterpret_cast<ThreadInfo*>(Arg);
+  TI->UserFn(TI->UserData);
+  return 0;
+}
+
+void llvm::llvm_execute_on_thread(void (*Fn)(void*), void *UserData,
+                                  unsigned RequestedStackSize) {
+  ThreadInfo Info = { Fn, UserData };
+  pthread_attr_t Attr;
+  pthread_t Thread;
+
+  // Construct the attributes object.
+  if (::pthread_attr_init(&Attr) != 0)
+    return;
+
+  // Set the requested stack size, if given.
+  if (RequestedStackSize != 0) {
+    if (::pthread_attr_setstacksize(&Attr, RequestedStackSize) != 0)
+      goto error;
+  }
+
+  // Construct and execute the thread.
+  if (::pthread_create(&Thread, &Attr, ExecuteOnThread_Dispatch, &Info) != 0)
+    goto error;
+
+  // Wait for the thread and clean up.
+  ::pthread_join(Thread, 0);
+  
+ error:
+  ::pthread_attr_destroy(&Attr);
+}
+
+#else
+
+// No non-pthread implementation, currently.
+
+void llvm::llvm_execute_on_thread(void (*Fn)(void*), void *UserData,
+                                  unsigned RequestedStackSize) {
+  (void) RequestedStackSize;
+  Fn(UserData);
+}
+
+#endif