code review 5279048: runtime: faster and more scalable GC

src/pkg/runtime/arm/atomic.c

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "runtime.h"
+#include "arch.h"
+
+static union {
+        Lock l;
+        byte pad [CacheLineSize];
+} locktab[57];
+
+#define LOCK(addr) (&locktab[((uintptr)addr>>3)%nelem(locktab)].l)
+
+// Atomic add and return new value.
+#pragma textflag 7
+uint32
+runtime·xadd(uint32 volatile *val, int32 delta)
+{
+        uint32 oval, nval;
+
+        for(;;){
+                oval = *val;
+                nval = oval + delta;
+                if(runtime·cas(val, oval, nval))
+                        return nval;
+        }
+}
+
+#pragma textflag 7
+uint32
+runtime·xchg(uint32 volatile* addr, uint32 v)
+{
+        uint32 old;
+
+        for(;;) {
+                old = *addr;
+                if(runtime·cas(addr, old, v))
+                        return old;
+        }
+}
+
+#pragma textflag 7
+void
+runtime·procyield(uint32 cnt)
+{
+        uint32 volatile i;
+
+        for(i = 0; i < cnt; i++) {
+        }
+}
+
+#pragma textflag 7
+uint32
+runtime·atomicload(uint32 volatile* addr)
+{
+        return runtime·xadd(addr, 0);
+}
+
+#pragma textflag 7
+void*
+runtime·atomicloadp(void* volatile* addr)
+{
+        return (void*)runtime·xadd((uint32 volatile*)addr, 0);
+}
+
+#pragma textflag 7
+void
+runtime·atomicstorep(void* volatile* addr, void* v)
+{
+        void *old;
+
+        for(;;) {
+                old = *addr;
+                if(runtime·casp(addr, old, v))
+                        return;
+        }
+}
+
+#pragma textflag 7
+void
+runtime·atomicstore(uint32 volatile* addr, uint32 v)
+{
+        uint32 old;
+
+        for(;;) {
+                old = *addr;
+                if(runtime·cas(addr, old, v))
+                        return;
+        }
+}
+
+#pragma textflag 7
+bool
+runtime·cas64(uint64 volatile *addr, uint64 *old, uint64 new)
+{
+        bool res;
+········
+        runtime·lock(LOCK(addr));
+        if(*addr == *old) {
+                *addr = new;
+                res = true;
+        } else {
+                *old = *addr;
+                res = false;
+        }
+        runtime·unlock(LOCK(addr));
+        return res;
+}
+
+#pragma textflag 7
+uint64
+runtime·xadd64(uint64 volatile *addr, int64 delta)
+{
+        uint64 res;
+········
+        runtime·lock(LOCK(addr));
+        res = *addr + delta;
+        *addr = res;
+        runtime·unlock(LOCK(addr));
+        return res;
+}
+
+#pragma textflag 7
+uint64
+runtime·atomicload64(uint64 volatile *addr)
+{
+        uint64 res;
+········
+        runtime·lock(LOCK(addr));
+        res = *addr;
+        runtime·unlock(LOCK(addr));
+        return res;
+}
+
+#pragma textflag 7
+void
+runtime·atomicstore64(uint64 volatile *addr, uint64 v)
+{
+        runtime·lock(LOCK(addr));
+        *addr = v;
+        runtime·unlock(LOCK(addr));
+}