Java immutable classes are much slower
I need some complex math libraries, so I hesitate to use immutable complex libraries and variable complex libraries Obviously, I want the computation to run fairly fast (unless it kills readability, etc.)
So I created a simple test speed variable vs immutable:
final class MutableInt {
private int value;
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
public MutableInt() {
this(0);
}
public MutableInt(int value) {
this.value = value;
}
}
final class ImmutableInt {
private final int value;
public ImmutableInt(int value) {
this.value = value;
}
public int getValue() {
return value;
}
}
public class TestImmutableSpeed {
static long testMutable(final int arrLen) {
MutableInt[] arrMutable = new MutableInt[arrLen];
for (int i = 0; i < arrMutable.length; ++i) {
arrMutable[i] = new MutableInt(i);
for (int j = 0; j < arrMutable.length; ++j) {
arrMutable[i].setValue(arrMutable[i].getValue() + j);
}
}
long sumMutable = 0;
for (MutableInt item : arrMutable) {
sumMutable += item.getValue();
}
return sumMutable;
}
static long testImmutable(final int arrLen) {
ImmutableInt[] arrImmutable = new ImmutableInt[arrLen];
for (int i = 0; i < arrImmutable.length; ++i) {
arrImmutable[i] = new ImmutableInt(i);
for (int j = 0; j < arrImmutable.length; ++j) {
arrImmutable[i] = new ImmutableInt(arrImmutable[i].getValue() + j);
}
}
long sumImmutable = 0;
for (ImmutableInt item : arrImmutable) {
sumImmutable += item.getValue();
}
return sumImmutable;
}
public static void main(String[] args) {
final int arrLen = 1<<14;
long tmStart = System.nanoTime();
System.out.println("sum = " + testMutable(arrLen));
long tmMid = System.nanoTime();
System.out.println("sum = " + testImmutable(arrLen));
long tmEnd = System.nanoTime();
System.out.println("speed comparison mutable vs immutable:");
System.out.println("mutable " + (tmMid - tmStart)/1000000 + " ms");
System.out.println("immutable " + (tmEnd - tmMid)/1000000 + " ms");
}
}
If the test runs too slowly / fast, you can resize the array
I run: - server - xms256m - XX: aggregateopts I get:
sum = 2199023247360 sum = 2199023247360 speed comparison mutable vs immutable: mutable 102 ms immutable 1506 ms
Question: do I lack some optimization parameters, or is the immutable version 15x slow?
If so, why do people write math libraries with immutable class complexity? Is it immutable, just "fancy" but useless?
I know that immutable classes are more secure or have no competition conditions for hash mapping keys, but these special cases can be handled unchanged anywhere
Editor: according to an answer suggestion, I rerun this micro benchmark with calipers. It runs 12 times faster than 15 times Change caliper benchmark Code:
import com.google.caliper.Runner;
import com.google.caliper.SimpleBenchmark;
final class MutableInt {
private int value;
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
public MutableInt() {
this(0);
}
public MutableInt(int value) {
this.value = value;
}
}
final class ImmutableInt {
private final int value;
public ImmutableInt(int value) {
this.value = value;
}
public int getValue() {
return value;
}
}
public class TestImmutableSpeed extends SimpleBenchmark {
static long testMutable(final int arrLen) {
MutableInt[] arrMutable = new MutableInt[arrLen];
for (int i = 0; i
Caliper output:
0% Scenario{vm=java,trial=0,benchmark=Mutable,type=-server,minMemory=-Xms256m,optimizations=-XX:+AggressiveOpts} 91614044.60 ns; ?=250338.20 ns @ 3 trials
50% Scenario{vm=java,benchmark=Immutable,optimizations=-XX:+AggressiveOpts} 1108057922.00 ns; ?=3920760.98 ns @ 3 trials
benchmark ms linear runtime
Mutable 91.6 ==
Immutable 1108.1 ==============================
Note that the optimization parameters for JVM output without caliper are:
0% Scenario{vm=java,benchmark=Mutable} 516562214.00 ns; ?=623120.57 ns @ 3 trials
50% Scenario{vm=java,benchmark=Immutable} 1706758503.00 ns; ?=5842389.60 ns @ 3 trials
benchmark ms linear runtime
Mutable 517 =========
Immutable 1707 ==============================
So bad parameters make both versions slow, but the ratio is not terrible (but not important)
Solution
It's fascinating, so first of all, it's not a fair test; When you do this, you won't heat the JVM Benchmarking is often difficult to do I refactor your code using Google caliper and get similar but different results; Invariant classes are only three times faster Do not know why? In any case, the work here so far:
TestImmutableSpeed. java
import com.google.caliper.Runner;
import com.google.caliper.SimpleBenchmark;
public class TestImmutableSpeed {
static final class MutableInt {
private int value;
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
public MutableInt() {
this(0);
}
public MutableInt(int value) {
this.value = value;
}
}
static final class ImmutableInt {
private final int value;
public ImmutableInt(int value) {
this.value = value;
}
public int getValue() {
return value;
}
}
public static class TestBenchmark extends SimpleBenchmark {
public void timeMutable(final int arrLen) {
MutableInt[] arrMutable = new MutableInt[arrLen];
for (int i = 0; i < arrMutable.length; ++i) {
arrMutable[i] = new MutableInt(i);
for (int j = 0; j < arrMutable.length; ++j) {
arrMutable[i].setValue(arrMutable[i].getValue() + j);
}
}
long sumMutable = 0;
for (MutableInt item : arrMutable) {
sumMutable += item.getValue();
}
System.out.println(sumMutable);
}
public void timeImmutable(final int arrLen) {
ImmutableInt[] arrImmutable = new ImmutableInt[arrLen];
for (int i = 0; i < arrImmutable.length; ++i) {
arrImmutable[i] = new ImmutableInt(i);
for (int j = 0; j < arrImmutable.length; ++j) {
arrImmutable[i] = new ImmutableInt(arrImmutable[i].getValue() + j);
}
}
long sumImmutable = 0;
for (ImmutableInt item : arrImmutable) {
sumImmutable += item.getValue();
}
System.out.println(sumImmutable);
}
}
public static void main(String[] args) {
Runner.main(TestBenchmark.class,new String[0]);
}
}
Caliper output
0% Scenario{vm=java,benchmark=Immutable} 78574.05 ns; σ=21336.61 ns @ 10 trials
50% Scenario{vm=java,benchmark=Mutable} 24956.94 ns; σ=7267.78 ns @ 10 trials
benchmark us linear runtime
Immutable 78.6 ==============================
Mutable 25.0 =========
vm: java
trial: 0
String update
So I was thinking about this more, and I decided to try to change the wrapped class from an int to an object, in this case a string Change the static class to a string and use integer valueOf(i). Tostring() loads strings instead of adding them, and attaches them to StringBuilder. I get the following results:
0% Scenario{vm=java,benchmark=Immutable} 11034616.91 ns; σ=7006742.43 ns @ 10 trials
50% Scenario{vm=java,benchmark=Mutable} 9494963.68 ns; σ=6201410.87 ns @ 10 trials
benchmark ms linear runtime
Immutable 11.03 ==============================
Mutable 9.49 =========================
vm: java
trial: 0
However, I think in this case, the difference is mainly the fact that all array replication must occur, not the use of strings