Guard dynamic library loading.
I did my best at implementing this for Win32, but I don't have a way to test it.
Can someone with access to a Win32 machine test/fix this?


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74188 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Win32/DynamicLibrary.inc b/lib/System/Win32/DynamicLibrary.inc
index 1ddf6ce..aa04268 100644
--- a/lib/System/Win32/DynamicLibrary.inc
+++ b/lib/System/Win32/DynamicLibrary.inc
@@ -67,6 +67,7 @@
                                     PVOID UserContext)
 #endif
   {
+    llvm::sys::SmartScopedWriter<true> Writer(&SymbolsLock);
     // Ignore VC++ runtimes prior to 7.1.  Somehow some of them get loaded
     // into the process.
     if (stricmp(ModuleName, "msvci70") != 0 &&
@@ -89,11 +90,13 @@
 }
 
 DynamicLibrary::DynamicLibrary() : handle(0) {
+  SmartScopedWriter<true> Writer(&SymbolsLock);
   handle = GetModuleHandle(NULL);
   OpenedHandles.push_back((HMODULE)handle);
 }
 
 DynamicLibrary::~DynamicLibrary() {
+  llvm::sys::SmartScopedWriter<true> Writer(&SymbolsLock);
   if (handle == 0)
     return;
 
@@ -113,8 +116,9 @@
 }
  
 bool DynamicLibrary::LoadLibraryPermanently(const char *filename,
-                                            std::string *ErrMsg) {
+                                            std::string *ErrMsg) {                                            
   if (filename) {
+    llvm::sys::SmartScopedWriter<true> Writer(&SymbolsLock);
     HMODULE a_handle = LoadLibrary(filename);
 
     if (a_handle == 0)
@@ -166,17 +170,24 @@
 
 void* DynamicLibrary::SearchForAddressOfSymbol(const char* symbolName) {
   // First check symbols added via AddSymbol().
-  std::map<std::string, void *>::iterator I = g_symbols().find(symbolName);
-  if (I != g_symbols().end())
+  SymbolsLock.reader_acquire();
+  std::map<std::string, void *>::iterator I = symbols.find(symbolName);
+  std::map<std::string, void *>::iterator E = symbols.end();
+  SymbolsLock.reader_release();
+  if (I != E)
     return I->second;
 
   // Now search the libraries.
+  SymbolsLock.writer_acquire();
   for (std::vector<HMODULE>::iterator I = OpenedHandles.begin(),
        E = OpenedHandles.end(); I != E; ++I) {
     FARPROC ptr = GetProcAddress((HMODULE)*I, symbolName);
-    if (ptr)
+    if (ptr) {
+      SymbolsLock.writer_release();
       return (void *) ptr;
+    }
   }
+  SymbolsLock.writer_release();
 
 #if defined(__MINGW32__)
   {