+FN_(takeMaybeMVarzh_fast)
+{
+ StgMVar *mvar;
+ StgClosure *val;
+ const StgInfoTable *info;
+
+ FB_
+ /* args: R1 = MVar closure */
+
+ mvar = (StgMVar *)R1.p;
+
+#ifdef SMP
+ info = LOCK_CLOSURE(mvar);
+#else
+ info = GET_INFO(mvar);
+#endif
+
+ if (info == &EMPTY_MVAR_info) {
+
+#ifdef SMP
+ /* unlock the MVar */
+ mvar->header.info = &EMPTY_MVAR_info;
+#endif
+
+ /* HACK: we need a pointer to pass back, so we abuse NO_FINALIZER_closure */
+ RET_NP(0, &NO_FINALIZER_closure);
+ }
+
+ val = mvar->value;
+ mvar->value = (StgClosure *)&END_TSO_QUEUE_closure;
+
+ /* do this last... we might have locked the MVar in the SMP case,
+ * and writing the info pointer will unlock it.
+ */
+ SET_INFO(mvar,&EMPTY_MVAR_info);
+
+ TICK_RET_UNBOXED_TUP(1);
+ RET_NP(1,val);
+ FE_
+}
+