Fix the ManagedStatic list ordering when using DynamicLibrary::addPermanentLibrary.

[marsupial]

Summary

r295737 included a fix for leaking libraries loaded via. DynamicLibrary::addPermanentLibrary.
This created a problem where static constructors in a library could insert llvm::ManagedStatic objects before DynamicLibrary would register it's own ManagedStatic, meaning a crash could occur at shutdown.

r301562 exasperated this problem by cleaning up the DynamicLibrary ManagedStatic during llvm_shutdown.

[efriedma]

lib/Support/DynamicLibrary.cpp

136

Why are you changing the scope of this lock? (What happens if a static constructor in a library calls getPermanentLibrary?)

[marsupial]

lib/Support/DynamicLibrary.cpp

136

The ManagedStatic OpenedHandles has a lock for construction.
The SymbolsMutex is the lock for adding to the list.
The way it was before it would be impossible for two threads to execute the DLOpen call in parallel.

[efriedma]

LGTM.

lib/Support/DynamicLibrary.cpp

136

Okay, that makes sense.

lib/Support/DynamicLibrary.cpp

 
 void DynamicLibrary::AddSymbol(StringRef SymbolName, void *SymbolValue) {
   SmartScopedLock<true> Lock(*SymbolsMutex);
   (*ExplicitSymbols)[SymbolName] = SymbolValue;
 }
 
 DynamicLibrary DynamicLibrary::getPermanentLibrary(const char *FileName,
                                                    std::string *Err) {
-  SmartScopedLock<true> Lock(*SymbolsMutex);
+  // Force OpenedHandles to be added into the ManagedStatic list before any
+  // ManagedStatic can be added from static constructors in HandleSet::DLOpen.
+  HandleSet& HS = *OpenedHandles;
+
   void *Handle = HandleSet::DLOpen(FileName, Err);
-  if (Handle != &Invalid)
-    OpenedHandles->AddLibrary(Handle, /*IsProcess*/ FileName == nullptr);
+  if (Handle != &Invalid) {
+    SmartScopedLock<true> Lock(*SymbolsMutex);
+    HS.AddLibrary(Handle, /*IsProcess*/ FileName == nullptr);
+  }
 
   return DynamicLibrary(Handle);
 }
 
 DynamicLibrary DynamicLibrary::addPermanentLibrary(void *Handle,
                                                    std::string *Err) {
   SmartScopedLock<true> Lock(*SymbolsMutex);
   // If we've already loaded this library, tell the caller.