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README.adoc

Chronicle Core

Maven Central javadoc

This library wraps up low level access to

System properties from file

The Jvm class in its static initialiser will load system properties from a file called system.properties if it can find this file in the current directory. If it can’t find this file in current directory it will look in .. too. This is a useful feature if you want to de-clutter your command line.

Chronicle Core class Jvm loads the file system.properties into the System’s properties. To ensure it is loaded early enough, add the following code to your Main

static {
    Jvm.init();
}

The choice of file to load can be overridden on the command line with -Dsystem.properties=my.properties

See Jvm.Main in the src/test as an example.

Off Heap Memory Access

This allows you to access native memory using primitives and some thread safe operations.

Memory memory = OS.memory();
long address = memory.allocate(1024);
try {
    memory.writeInt(address, 1);
    assert memory.readInt(address) == 1;
    final boolean swapped = memory.compareAndSwapInt(address, 1, 2);
    assert swapped;
    assert memory.readInt(address) == 2;
} finally {
    memory.freeMemory(address, 1024);
}

JVM Access Methods

Check the JVM is running in debug mode

if (Jvm.isDebug()) {
   // running in debug.

Rethrow a checked exception as an unchecked one.

try {
    // IO operation
} catch (IOException ioe) {
    throw Jvm.rethrow(ioe);
}

Get a Field for a Class by name

Field theUnsafe = Jvm.getField(Unsafe.class, "theUnsafe");
Unsafe unsafe = (Unsafe) theUnsafe.get(null);

OS Calls

Access to system calls

int processId = OS.getProcessId();
int maxProcessId = OS.getMaxProcessId();
int pageSize = OS.getPageSize();
boolean isWindows = OS.isWindows();
boolean is64bit = OS.is64Bit();
String hostname = OS.getHostName();
String username = OS.getUserName();
String targetDir = OS.getTarget(); // where is the target directory during builds.

Memory mapped files

FileChannel fc = new CleaningRandomAccessFile(fileName, "rw").getChannel();
// map in 64 KiB
long address = OS.map(fc, MapMode.READ_WRITE, 0, 64 << 10);
// use address
OS.memory().writeLong(1024L, 0x1234567890ABCDEFL);
// unmap memory region
OS.unmap(address, 64 << 10);

Deterministic Resource Management

Component which are closeable or reference counted can be released deterministically without waiting for a GC.

Closeable Resources

A Closeable resources has a simple lifecycle. It is open when created, and cannot be used once closed.

public class AbstractCloseableTest {

    @Test
    public void close() {
        MyCloseable mc = new MyCloseable();
        assertFalse(mc.isClosed());
        assertEquals(0, mc.performClose);

        mc.throwExceptionIfClosed();

 mc.close();
        assertTrue(mc.isClosed());
        assertEquals(1, mc.performClose);

        mc.close();
        assertTrue(mc.isClosed());
        assertEquals(1, mc.performClose);
    }

    @Test(expected = IllegalStateException.class)
    public void throwExceptionIfClosed() {
        MyCloseable mc = new MyCloseable();
        mc.close();
        mc.throwExceptionIfClosed();

 }

    @Test
    public void warnAndCloseIfNotClosed() {
        Map<ExceptionKey, Integer> map = Jvm.recordExceptions();
        MyCloseable mc = new MyCloseable();
        mc.warnAndCloseIfNotClosed();
        Jvm.resetExceptionHandlers();
        assertEquals("Discarded without closing\n" +
                        "java.lang.IllegalStateException: net.openhft.chronicle.core.StackTrace: Created Here",
                map.keySet().stream()
                        .map(e -> e.message + "\n" + e.throwable)
                        .collect(Collectors.joining(", ")));
    }

    static class MyCloseable extends AbstractCloseable {
        int performClose;

        @Override
        protected void performClose() {
            performClose++;
        }
    }
}

Resource Reference Counting

Use reference counting to deterministically release resources.

A reference counted resource can add reservations until closed.

public class AbstractReferenceCountedTest {

    @Test
    public void reserve() {
        assertTrue(Jvm.isResourceTracing());
        MyReferenceCounted rc = new MyReferenceCounted();
        assertEquals(1, rc.refCount());

        ReferenceOwner a = ReferenceOwner.temporary("a");
        rc.reserve(a);
        assertEquals(2, rc.refCount());

        ReferenceOwner b = ReferenceOwner.temporary("b");
        rc.reserve(b);
        assertEquals(3, rc.refCount());

        try {
            rc.reserve(a);
            fail();
        } catch (IllegalStateException ignored) {
        }
        assertEquals(3, rc.refCount());

        rc.release(b);
        assertEquals(2, rc.refCount());

        rc.release(a);
        assertEquals(1, rc.refCount());
        assertEquals(0, rc.performRelease);

        rc.releaseLast();
        assertEquals(0, rc.refCount());
        assertEquals(1, rc.performRelease);
    }

@Test
    public void reserveWhenClosed() {
        MyReferenceCounted rc = new MyReferenceCounted();
        assertEquals(1, rc.refCount());

        ReferenceOwner a = ReferenceOwner.temporary("a");
        rc.reserve(a);
        assertEquals(2, rc.refCount());

        assertFalse(rc.isClosed());

        rc.closeable.close();

        assertEquals(2, rc.refCount());
        assertTrue(rc.isClosed());

        ReferenceOwner b = ReferenceOwner.temporary("b");
        try {
            rc.reserve(b);
            fail();
        } catch (IllegalStateException ignored) {
        }
        assertEquals(2, rc.refCount());

        assertFalse(rc.tryReserve(b));
        assertEquals(2, rc.refCount());

        rc.release(a);
        assertEquals(1, rc.refCount());
        assertEquals(0, rc.performRelease);

        rc.throwExceptionIfReleased();

        rc.releaseLast();
        assertEquals(0, rc.refCount());
        assertEquals(1, rc.performRelease);

        rc.throwExceptionBadResourceOwner();
        try {
            rc.throwExceptionIfClosed();

 fail();
        } catch (IllegalStateException ignored) {

        }
        try {
            rc.throwExceptionIfReleased();
            fail();
        } catch (IllegalStateException ignored) {

        }
    }

    @Test
    public void throwExceptionBadResourceOwner() {
        MyReferenceCounted rc = new MyReferenceCounted();
        MyReferenceCounted rc2 = new MyReferenceCounted();
        rc.reserve(rc2);
        rc.throwExceptionBadResourceOwner();

        rc2.closeable.close();
        try {
            rc.throwExceptionBadResourceOwner();
            fail();
        } catch (IllegalStateException ignored) {
        }
        rc.release(rc2);
        rc.releaseLast();
    }

    @Test
    public void throwExceptionIfClosed() {
        MyReferenceCounted rc = new MyReferenceCounted();
        rc.throwExceptionIfClosed();

 rc.closeable.close();
        try {
            rc.throwExceptionIfClosed();

 fail();
        } catch (IllegalStateException ignored) {

        }
    }

    static class MyReferenceCounted extends AbstractReferenceCounted {
        final AbstractCloseable closeable;
        int performRelease;

        public MyReferenceCounted() {
            this(new AbstractCloseableTest.MyCloseable());
        }

        public MyReferenceCounted(AbstractCloseable abstractCloseable) {
            super(abstractCloseable);
            closeable = abstractCloseable;
        }

        @Override
        protected void performRelease() {
            performRelease++;
        }
    }
}
MappedFile mf = MappedFile.mappedFile(tmp, chunkSize, 0);
MappedBytesStore bs = mf.acquireByteStore(chunkSize + (1 << 10));

assertEquals(2, mf.refCount());
assertEquals(3, bs.refCount());
assertEquals("refCount: 2, 0, 3", mf.referenceCounts());

mf.close();
assertEquals(2, bs.refCount());
assertEquals("refCount: 1, 0, 2", mf.referenceCounts());
bs2.releaseLast();
assertEquals(1, mf.refCount());
assertEquals(1, bs.refCount());
bs.releaseLast();
assertEquals(0, bs.refCount());
assertEquals(0, mf.refCount());
assertEquals("refCount: 0, 0, 0", mf.referenceCounts());

Object Pools

There is String and Enum object pools to turn a CharSequence into a String.

Bytes b = Bytes.from("Hello World");
b.readSkip(6);

StringInterner si = new StringInterner(128);
String s = si.intern(b);
String s2 = si.intern(b);
assertEquals("World", s);
assertSame(s, s2);

Class Local Caching

Add caching of a data structure for each class using a lambda

public static final ClassLocal<EnumInterner> ENUM_INTERNER =
        ClassLocal.withInitial(c -> new EnumInterner<>(c));

E enumValue = ENUM_INTERNER.get(enumClass).intern(stringBuilder);

Maths Functions

Maths functions to support rounds

double a = 0.1;
double b = 0.3;
double c= Maths.round2(b - a); // 0.2 rounded to 2 decimal places

Checking type conversions

int i = Maths.toInt32(longValue);

Serializable Lambdas

There is a number of FunctionalInterfaces you can utilise as method arguments. This allows implicitly making a lambda Serializable.

// in KeyedVisitable
default <R> R applyToKey(K key, @NotNull SerializableFunction<E, R> function) {

// in code

String fullename = map.applyToKey("u:123223", u -> u.getFullName());

Histogram

A high dynamic range histogram with tunable accuracy.

Histogram h = new Histogram(32, 4);
long start = instance.ticks(), prev = start;
for (int i = 0; i <= 1000_000_000; i++) {
    long now = instance.ticks();
    long time = now - prev;
    h.sample(time);
    prev = now;
}
System.out.println(h.toLongMicrosFormat(instance::toMicros));

JLBH

JLBH has moved home and now lives in its own project, see JLBH.

Loop Block Monitor tool

The tool to summarise the thread stack traces is here.

net.openhft.chronicle.core.threads.MonitorProfileAnalyserMain

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