This library wraps up low level access to
- Off Heap Memory Access
- JVM Access Methods
- OS Calls
- Resource Reference Counting
- Object Pools
- Class Local Caching
- Maths Functions for casting types, rounding double, faster hashing.
- Serializable Lambdas
- Histogram A high performance wide range histogram.
This allows you to access native memory using primitives and some thread safe operations.
Memory m = OS.memory();
try {
long addr = m.allocate(1024);
m.writeInt(0L, 1);
boolean b = m.compareAndSwap(0L, 1, 2);
assert b;
} finally {
m.free(addr);
}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);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
FileChanel fc = new RandomAccessFile(fileName, "rw").getFileChannel();
// 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);Use reference counting to deterministically release resources.
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.release();
assertEquals(1, mf.refCount());
assertEquals(1, bs.refCount());
bs.release();
assertEquals(0, bs.refCount());
assertEquals(0, mf.refCount());
assertEquals("refCount: 0, 0, 0", mf.referenceCounts());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);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 to support rounds
double a = 0.1;
double b = 0.3;
double c= Maths.round2(b - a); // 0.2 rounded to 2 decimal placesChecking type conversions
int i = Maths.toInt32(longValue);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());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));