Fix two small issues in the runtime

     1) Perf fix for thread attach during GC.  The runtime holds the ThreadStore's ReaderWriterLock for the entire duration of a suspend-for-GC.  This causes new threads to spin in the RWL code waiting on the GC to finish.  I have added a check that shortcuts to the proper wait-on-an-event in this case.

     2) Fix RhpCheckCctor2__SlowPath to properly preserve stack alignment on AMD64.  This was found while experimenting with a PGO instrumented build of the runtime.

[tfs-changeset: 1602614]

1 files changed, 7 insertions, 0 deletions

diff --git a/src/Native/Runtime/threadstore.cpp b/src/Native/Runtime/threadstore.cpp
index 2094a0c72..26403e0f5 100644
--- a/src/Native/Runtime/threadstore.cpp
+++ b/src/Native/Runtime/threadstore.cpp
@@ -138,6 +138,13 @@ void ThreadStore::AttachCurrentThread(bool fAcquireThreadStoreLock)
     pAttachingThread->Construct();
     ASSERT(pAttachingThread->m_ThreadStateFlags == Thread::TSF_Unknown);
 
+    // The runtime holds the thread store lock for the duration of thread suspension for GC, so let's check to 
+    // see if that's going on and, if so, use a proper wait instead of the RWL's spinning.  NOTE: when we are 
+    // called with fAcquireThreadStoreLock==false, we are being called in a situation where the GC is trying to 
+    // init a GC thread, so we must honor the flag to mean "do not block on GC" or else we will deadlock.
+    if (fAcquireThreadStoreLock && (RhpTrapThreads != 0))
+        RedhawkGCInterface::WaitForGCCompletion();
+
     ThreadStore* pTS = GetThreadStore();
     ReaderWriterLock::WriteHolder write(&pTS->m_Lock, fAcquireThreadStoreLock);