make thread_term @nogc

- needed to replace destroy with manual destruction
- use custom monitor deletion that does not call any event hooks

Author: MartinNowak

src/core/thread.d

@@ -1736,7 +1736,7 @@ private:
         }
     }
 
-    static void termLocks()
+    static void termLocks() @nogc
     {
         foreach (ref lock; _locks)
             (cast(Mutex)lock.ptr).__dtor();
@@ -2090,20 +2090,28 @@ extern (C) void thread_init() @nogc
         status = sem_init( &suspendCount, 0, 0 );
         assert( status == 0 );
     }
-    __gshared align(Thread.alignof) void[__traits(classInstanceSize, Thread)] mainThread;
     if (typeid(Thread).initializer.ptr)
-        mainThread[] = typeid(Thread).initializer[];
-    Thread.sm_main = attachThread((cast(Thread)mainThread.ptr).__ctor());
+        _mainThreadStore[] = typeid(Thread).initializer[];
+    Thread.sm_main = attachThread((cast(Thread)_mainThreadStore.ptr).__ctor());
 }
 
+private __gshared align(Thread.alignof) void[__traits(classInstanceSize, Thread)] _mainThreadStore;
+
+extern (C) void _d_monitordelete_nogc(Object h) @nogc;
 
 /**
  * Terminates the thread module. No other thread routine may be called
  * afterwards.
  */
-extern (C) void thread_term()
+extern (C) void thread_term() @nogc
 {
-    destroy(Thread.sm_main);
+    assert(_mainThreadStore.ptr is cast(void*) Thread.sm_main);
+
+    // destruct manually as object.destroy is not @nogc
+    Thread.sm_main.__dtor();
+    _d_monitordelete_nogc(Thread.sm_main);
+    if (typeid(Thread).initializer.ptr)
+        _mainThreadStore[] = typeid(Thread).initializer[];
     Thread.sm_main = null;
 
     assert(Thread.sm_tbeg && Thread.sm_tlen == 1);

src/rt/monitor_.d

@@ -56,6 +56,26 @@ extern (C) void _d_monitordelete(Object h, bool det)
     }
 }
 
+// does not call dispose events, for internal use only
+extern (C) void _d_monitordelete_nogc(Object h) @nogc
+{
+    auto m = getMonitor(h);
+    if (m is null)
+        return;
+
+    if (m.impl)
+    {
+        // let the GC collect the monitor
+        setMonitor(h, null);
+    }
+    else if (!atomicOp!("-=")(m.refs, cast(size_t) 1))
+    {
+        // refcount == 0 means unshared => no synchronization required
+        deleteMonitor(cast(Monitor*) m);
+        setMonitor(h, null);
+    }
+}
+
 extern (C) void _d_monitorenter(Object h)
 in
 {
@@ -173,6 +193,7 @@ else version (Posix)
 {
     import core.sys.posix.pthread;
 
+@nogc:
     alias Mutex = pthread_mutex_t;
     __gshared pthread_mutexattr_t gattr;
 
@@ -211,17 +232,17 @@ struct Monitor
 
 private:
 
-@property ref shared(Monitor*) monitor(Object h) pure nothrow
+@property ref shared(Monitor*) monitor(Object h) pure nothrow @nogc
 {
     return *cast(shared Monitor**)&h.__monitor;
 }
 
-private shared(Monitor)* getMonitor(Object h) pure
+private shared(Monitor)* getMonitor(Object h) pure @nogc
 {
     return atomicLoad!(MemoryOrder.acq)(h.monitor);
 }
 
-void setMonitor(Object h, shared(Monitor)* m) pure
+void setMonitor(Object h, shared(Monitor)* m) pure @nogc
 {
     atomicStore!(MemoryOrder.rel)(h.monitor, m);
 }
@@ -263,7 +284,7 @@ shared(Monitor)* ensureMonitor(Object h)
     }
 }
 
-void deleteMonitor(Monitor* m)
+void deleteMonitor(Monitor* m) @nogc
 {
     destroyMutex(&m.mtx);
     free(m);