[Local GC] Unify background GC thread and server GC thread creation (#14821)

* Initial cut, ignoring thread affinity

* Integrate thread affinity

* Affinity for standalone Windows

* Add 'specialness' and the thread name as arguments to CreateThread

* First crack at unified implementation

* Set priority for server GC threads

* Remove unused parameter

* Address code review feedback and remove some dead code that broke the clang build

* Use char* on the interface instead of wchar_t (doesn't play well cross-platform)

* Rename IsGCSpecialThread -> CurrentThreadWasCreatedByGC

* Code review feedback and fix up the build

* rename CurrentThreadWasCreatedByGC -> WasCurrentThreadCreatedByGC

* Fix a contract violation when converting string encodings

* Thread::CreateUtilityThread returns a thread that is not suspended - restarting a non-suspended thread is incorrect

* CreateUnsuspendableThread -> CreateNonSuspendableThread

1 files changed, 26 insertions, 9 deletions

diff --git a/src/gc/gcinterface.ee.h b/src/gc/gcinterface.ee.h
index d65da60678..84578b6d8a 100644
--- a/src/gc/gcinterface.ee.h
+++ b/src/gc/gcinterface.ee.h
@@ -79,6 +79,9 @@ public:
 
     // Gets the Thread instance for the current thread, or null if no thread
     // instance is associated with this thread.
+    //
+    // If the GC created the current thread, GetThread returns null for threads
+    // that were not created as suspendable (see `IGCHeap::CreateThread`).
     virtual
     Thread* GetThread() = 0;
 
@@ -98,9 +101,21 @@ public:
     virtual
     void GcEnumAllocContexts(enum_alloc_context_func* fn, void* param) = 0;
 
-    // Creates and returns a new background thread.
-    virtual
-    Thread* CreateBackgroundThread(GCBackgroundThreadFunction threadStart, void* arg) = 0;
+    // Creates and returns a new thread.
+    // Parameters:
+    //  threadStart - The function that will serve as the thread stub for the
+    //                new thread. It will be invoked immediately upon the
+    //                new thread upon creation.
+    //  arg - The argument that will be passed verbatim to threadStart.
+    //  is_suspendable - Whether or not the thread that is created should be suspendable
+    //                   from a runtime perspective. Threads that are suspendable have
+    //                   a VM Thread object associated with them that can be accessed
+    //                   using `IGCHeap::GetThread`.
+    //  name - The name of this thread, optionally used for diagnostic purposes.
+    // Returns:
+    //  true if the thread was started successfully, false if not.
+    virtual
+    bool CreateThread(void (*threadStart)(void*), void* arg, bool is_suspendable, const char* name) = 0;
 
     // When a GC starts, gives the diagnostics code a chance to run.
     virtual
@@ -192,16 +207,18 @@ public:
     virtual
     void FreeStringConfigValue(const char* value) = 0;
 
-    // Asks the EE about whether or not the current thread is a GC thread:
-    // a server GC thread, background GC thread, or the thread that suspended
-    // the EE at the start of a GC.
+    // Returns true if this thread is a "GC thread", or a thread capable of
+    // doing GC work. Threads are either /always/ GC threads
+    // (if they were created for this purpose - background GC threads
+    // and server GC threads) or they became GC threads by suspending the EE
+    // and initiating a collection.
     virtual
     bool IsGCThread() = 0;
 
-    // Asks the EE about whether or not the current thread is a GC "special"
-    // thread: a server GC thread or a background GC thread.
+    // Returns true if the current thread is either a background GC thread
+    // or a server GC thread.
     virtual
-    bool IsGCSpecialThread() = 0;
+    bool WasCurrentThreadCreatedByGC() = 0;
 };
 
 #endif // _GCINTERFACE_EE_H_