[Windows] Use TerminateProcess to exit without running destructors

[mstorsjo]

Summary

If exiting using _Exit or ExitProcess, DLLs are still unloaded
cleanly before exiting, running destructors and other cleanup in those
DLLs. When the caller expects to exit without cleanup, running
destructors in some loaded DLLs (which can be either libLLVM.dll or
e.g. libc++.dll) can cause deadlocks occasionally.

This is an alternative to D102684.

[rnk]

lgtm

Yep, this is more or less exactly what I had in mind. :)

[mstorsjo]

Let's hope this one puts the issue at rest, finally, then :-)

I'll push it tomorrow or so.

[mati865]

Feels like a heavy hammer to me but guess there is no better option.

[mstorsjo]

In D102944#2774998, @mati865 wrote:

Feels like a heavy hammer to me but guess there is no better option.

Well the whole early exit codepath in lld is a pretty special construct too, and I guess this is the closest match to the wanted behavior of ‘_Exit’ on windows...

llvm/include/llvm/Support/Process.h

public:
   static unsigned GetRandomNumber();
 
   /// Equivalent to ::exit(), except when running inside a CrashRecoveryContext.
   /// In that case, the control flow will resume after RunSafely(), like for a
   /// crash, rather than exiting the current process.
   /// Use \arg NoCleanup for calling _exit() instead of exit().
   LLVM_ATTRIBUTE_NORETURN
   static void Exit(int RetCode, bool NoCleanup = false);
+
+private:
+  LLVM_ATTRIBUTE_NORETURN
+  static void ExitNoCleanup(int RetCode);
 };
 
 }
 }
 
 #endif

llvm/lib/Support/Process.cpp

 bool Process::AreCoreFilesPrevented() { return coreFilesPrevented; }
 
 LLVM_ATTRIBUTE_NORETURN
 void Process::Exit(int RetCode, bool NoCleanup) {
   if (CrashRecoveryContext *CRC = CrashRecoveryContext::GetCurrent())
     CRC->HandleExit(RetCode);
 
   if (NoCleanup)
-    _Exit(RetCode);
+    ExitNoCleanup(RetCode);
   else
     ::exit(RetCode);
 }
 
 // Include the platform-specific parts of this class.
 #ifdef LLVM_ON_UNIX
 #include "Unix/Process.inc"
 #endif
 #ifdef _WIN32
 #include "Windows/Process.inc"
 #endif

llvm/lib/Support/Unix/Process.inc

 #if HAVE_DECL_ARC4RANDOM
   return arc4random();
 #else
   static int x = (static_cast<void>(::srand(GetRandomNumberSeed())), 0);
   (void)x;
   return ::rand();
 #endif
 }
+
+LLVM_ATTRIBUTE_NORETURN
+void Process::ExitNoCleanup(int RetCode) { _Exit(RetCode); }

llvm/lib/Support/Windows/Process.inc

llvm::VersionTuple llvm::GetWindowsOSVersion() {
   }
   return llvm::VersionTuple(0, 0, 0, 0);
 }
 
 bool llvm::RunningWindows8OrGreater() {
   // Windows 8 is version 6.2, service pack 0.
   return GetWindowsOSVersion() >= llvm::VersionTuple(6, 2, 0, 0);
 }
+
+LLVM_ATTRIBUTE_NORETURN
+void Process::ExitNoCleanup(int RetCode) {
+  TerminateProcess(GetCurrentProcess(), RetCode);
+  llvm_unreachable("TerminateProcess doesn't return");
+}