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Scan _isAscii through a byteArrayViewVarHandle instead of Unsafe.getLong #15

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Merged
merlimat merged 1 commit into from
Jul 30, 2026
Merged

Scan _isAscii through a byteArrayViewVarHandle instead of Unsafe.getLong #15

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37 changes: 17 additions & 20 deletions code-generator/src/main/resources/io/streamnative/lightproto/generator/LightProtoCodec.java
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,6 @@ class LightProtoCodec {
private static final MethodHandle MH_GET_OBJECT;
private static final MethodHandle MH_PUT_OBJECT;
private static final MethodHandle MH_COPY_MEMORY;
private static final MethodHandle MH_GET_LONG;
private static final MethodHandle MH_ALLOCATE_INSTANCE;

static {
Expand All @@ -53,7 +52,6 @@ class LightProtoCodec {
MethodHandle mhGetObject = null;
MethodHandle mhPutObject = null;
MethodHandle mhCopyMemory = null;
MethodHandle mhGetLong = null;
MethodHandle mhAllocateInstance = null;
try {
Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
Expand Down Expand Up @@ -82,8 +80,6 @@ class LightProtoCodec {
mhCopyMemory = lookup.unreflect(
unsafeClass.getMethod("copyMemory", Object.class, long.class, Object.class, long.class, long.class))
.bindTo(unsafe);
mhGetLong = lookup.unreflect(
unsafeClass.getMethod("getLong", Object.class, long.class)).bindTo(unsafe);
mhAllocateInstance = lookup.unreflect(
unsafeClass.getMethod("allocateInstance", Class.class)).bindTo(unsafe);
hasUnsafe = true;
Expand All @@ -97,7 +93,6 @@ class LightProtoCodec {
MH_GET_OBJECT = mhGetObject;
MH_PUT_OBJECT = mhPutObject;
MH_COPY_MEMORY = mhCopyMemory;
MH_GET_LONG = mhGetLong;
MH_ALLOCATE_INSTANCE = mhAllocateInstance;
}

Expand Down Expand Up @@ -548,24 +543,26 @@ static String readString(ByteBuf b, int index, int len) {
return b.toString(index, len, StandardCharsets.UTF_8);
}

// Plain unfenced 8-byte loads. The former sun.misc.Unsafe.getLong version
// executed a JDK 24+ acquire-load per call (JEP 498), whose cost grows with
// the store traffic of whatever ran just before — measured as a large part
// of string-materialization time right after a parse.
private static final java.lang.invoke.VarHandle LONG_ARRAY_VIEW =
MethodHandles.byteArrayViewVarHandle(long[].class, java.nio.ByteOrder.nativeOrder());

private static boolean _isAscii(byte[] bytes, int len) {
try {
// Check 8 bytes at a time using long reads — data is in L1 cache from the copy
int i = 0;
for (; i + 7 < len; i += 8) {
if (((long) MH_GET_LONG.invokeExact((Object) bytes, BYTE_ARRAY_BASE_OFFSET + i)
& 0x8080808080808080L) != 0) {
return false;
}
}
// Check remaining bytes
for (; i < len; i++) {
if (bytes[i] < 0) return false;
// Check 8 bytes at a time using long reads — data is in L1 cache from the copy
int i = 0;
for (; i + 7 < len; i += 8) {
if (((long) LONG_ARRAY_VIEW.get(bytes, i) & 0x8080808080808080L) != 0) {
return false;
}
return true;
} catch (Throwable t) {
throw new RuntimeException(t);
}
// Check remaining bytes
for (; i < len; i++) {
if (bytes[i] < 0) return false;
}
return true;
}

static void skipUnknownField(int tag, ByteBuf buffer) {
Expand Down
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