我已經成立了一個JMH基準來衡量什麼是從一個空數組空,System.arraycopy
更快Arrays.fill
,zeroying一個DirectByteBuffer或zeroying一個unsafe
的內存塊試圖回答這個question 讓我們拋開這zeroying直接分配的內存是一種罕見的情況,並討論我的基準測試結果。爲什麼直接內存「數組」比通常的Java數組更慢?
這裏的江鈴控股的基準片斷(full code available via a gist)包括unsafe.setMemory
情況下,由@apangin在原崗位,byteBuffer.put(byte[], offset, length)
和longBuffer.put(long[], offset, length)
的建議由@揚·舍費爾的建議:
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void arrayFill() {
Arrays.fill(objectHolderForFill, null);
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void arrayCopy() {
System.arraycopy(nullsArray, 0, objectHolderForArrayCopy, 0, objectHolderForArrayCopy.length);
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void directByteBufferManualLoop() {
while (referenceHolderByteBuffer.hasRemaining()) {
referenceHolderByteBuffer.putLong(0);
}
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void directByteBufferBatch() {
referenceHolderByteBuffer.put(nullBytes, 0, nullBytes.length);
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void directLongBufferManualLoop() {
while (referenceHolderLongBuffer.hasRemaining()) {
referenceHolderLongBuffer.put(0L);
}
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void directLongBufferBatch() {
referenceHolderLongBuffer.put(nullLongs, 0, nullLongs.length);
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void unsafeArrayManualLoop() {
long addr = referenceHolderUnsafe;
long pos = 0;
for (int i = 0; i < size; i++) {
unsafe.putLong(addr + pos, 0L);
pos += 1 << 3;
}
}
@Benchmark
@BenchmarkMode(Mode.SampleTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public void unsafeArraySetMemory() {
unsafe.setMemory(referenceHolderUnsafe, size*8, (byte) 0);
}
這裏是我(的Java 1.8 ,江鈴控股1.13,酷睿i3-6100U 2.30 GHz時,Win10):
100 elements
Benchmark Mode Cnt Score Error Units
ArrayNullFillBench.arrayCopy sample 5234029 39,518 ± 0,991 ns/op
ArrayNullFillBench.directByteBufferBatch sample 6271334 43,646 ± 1,523 ns/op
ArrayNullFillBench.directLongBufferBatch sample 4615974 45,252 ± 2,352 ns/op
ArrayNullFillBench.arrayFill sample 4745406 76,997 ± 3,547 ns/op
ArrayNullFillBench.unsafeArrayManualLoop sample 5980381 78,811 ± 2,870 ns/op
ArrayNullFillBench.unsafeArraySetMemory sample 5985884 85,062 ± 2,096 ns/op
ArrayNullFillBench.directLongBufferManualLoop sample 4697023 116,242 ± 2,579 ns/op WOW
ArrayNullFillBench.directByteBufferManualLoop sample 7504629 208,440 ± 10,651 ns/op WOW
I skipped all the loop implementations (except arrayFill for scale) from further tests
1000 elements
Benchmark Mode Cnt Score Error Units
ArrayNullFillBench.arrayCopy sample 6780681 184,516 ± 14,036 ns/op
ArrayNullFillBench.directLongBufferBatch sample 4018778 293,325 ± 4,074 ns/op
ArrayNullFillBench.directByteBufferBatch sample 4063969 313,171 ± 4,861 ns/op
ArrayNullFillBench.arrayFill sample 6862928 518,886 ± 6,372 ns/op
10000 elements
Benchmark Mode Cnt Score Error Units
ArrayNullFillBench.arrayCopy sample 2551851 2024,543 ± 12,533 ns/op
ArrayNullFillBench.directLongBufferBatch sample 2958517 4469,210 ± 10,376 ns/op
ArrayNullFillBench.directByteBufferBatch sample 2892258 4526,945 ± 33,443 ns/op
ArrayNullFillBench.arrayFill sample 5689507 5028,592 ± 9,074 ns/op
能否請您澄清以下幾個問題:
1. Why `unsafeArraySetMemory` is a bit but slower than `unsafeArrayManualLoop`?
2. Why directByteBuffer is 2.5X-5X slower than others?
如果你不介意我已經糾正了我的帖子,以消除這個'數量級'混亂:-)感謝您指出,我已經標記爲asnwer有用。 – bashnesnos