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package org.openjdk.bench.vm.compiler;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.CompilerControl;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;

import java.util.Random;
import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
@Warmup(iterations = 4, time = 2, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 4, time = 2, timeUnit = TimeUnit.SECONDS)
@Fork(value = 3)
public abstract class WriteBarrier {

    // For array references
    public static final int NUM_REFERENCES_SMALL = 32;
    public static final int NUM_REFERENCES_LARGE = 2048;

    // For array update tests
    private Object[] theArraySmall;
    private int[] indicesSmall;

    private Object[] theArrayLarge;
    private int[] indicesLarge;

    private Object nullRef;
    private Object realRef;

    // For field update tests
    public Referencer head = null;
    public Referencer tail = null;

    // For random number generation
    private int m_w;
    private int m_z;

    // For field references
    public class Referencer {
        Referencer next = null;
        Referencer() {
            this.next = null;
        }
        void append(Referencer r) {
            this.next = r;
        }
        void clear() {
            this.next = null;
        }
    }

    @Setup
    public void setup() {
        theArraySmall = new Object[NUM_REFERENCES_SMALL];
        indicesSmall = new int[NUM_REFERENCES_SMALL];

        theArrayLarge = new Object[NUM_REFERENCES_LARGE];
        indicesLarge = new int[NUM_REFERENCES_LARGE];

        m_w = (int) System.currentTimeMillis();
        Random random = new Random();
        m_z = random.nextInt(10000) + 1;

        for (int i = 0; i < NUM_REFERENCES_SMALL; i++) {
            indicesSmall[i] = get_random() % (NUM_REFERENCES_SMALL - 1);
        }

        for (int i = 0; i < NUM_REFERENCES_LARGE; i++) {
            indicesLarge[i] = get_random() % (NUM_REFERENCES_LARGE - 1);
        }

        realRef = new Object();

        // Build a small linked structure
        this.head = new Referencer();
        this.tail = new Referencer();
        this.head.append(this.tail);

        // This will (hopefully) promote objects to old space
        // Run with -XX:+DisableExplicitGC to keep
        // objects in young space
        System.gc();
    }

    private int get_random() {
        m_z = 36969 * (m_z & 65535) + (m_z >> 16);
        m_w = 18000 * (m_w & 65535) + (m_w >> 16);
        return Math.abs((m_z << 16) + m_w);  /* 32-bit result */
    }

    // This and the other testArrayWriteBarrierFast benchmarks below should not
    // be inlined into the JMH-generated harness method. If the methods were
    // inlined, we might spill in the main loop (on x64) depending on very
    // subtle conditions (such as whether LinuxPerfAsmProfiler is enabled!),
    // which could distort the results.
    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void testArrayWriteBarrierFastPathRealSmall() {
        for (int i = 0; i < NUM_REFERENCES_SMALL; i++) {
            theArraySmall[indicesSmall[NUM_REFERENCES_SMALL - i - 1]] = realRef;
        }
    }

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void testArrayWriteBarrierFastPathNullSmall() {
        for (int i = 0; i < NUM_REFERENCES_SMALL; i++) {
            theArraySmall[indicesSmall[NUM_REFERENCES_SMALL - i - 1]] = nullRef;
        }
    }

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void testArrayWriteBarrierFastPathRealLarge() {
        for (int i = 0; i < NUM_REFERENCES_LARGE; i++) {
            theArrayLarge[indicesLarge[NUM_REFERENCES_LARGE - i - 1]] = realRef;
        }
    }

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void testArrayWriteBarrierFastPathNullLarge() {
        for (int i = 0; i < NUM_REFERENCES_LARGE; i++) {
            theArrayLarge[indicesLarge[NUM_REFERENCES_LARGE - i - 1]] = nullRef;
        }
    }

    @Benchmark()
    public void testFieldWriteBarrierFastPath() {
        // Shuffle everything around
        this.tail.append(this.head);
        this.head.clear();
        this.head.append(this.tail);
        this.tail.clear();
    }

    // This run is useful to compare different GC barrier models without being
    // affected by C2 unrolling the main loop differently for each model.
    @Fork(value = 3, jvmArgs = {"-XX:LoopUnrollLimit=1"})
    public static class WithoutUnrolling extends WriteBarrier {}

    // This run is useful to study the interaction of GC barriers and loop
    // unrolling. Check that the main loop in the testArray benchmarks is
    // unrolled (or not) as expected for the studied GC barrier model.
    @Fork(value = 3)
    public static class WithDefaultUnrolling extends WriteBarrier {}
}
