nitsanw

# {method} 'poll' '()Ljava/lang/Object;' in 'io/jaq/spsc/FFBuffer' BEFORE
  #           [sp+0x20]  (sp of caller)
  0x00007facb1060c80: mov    r10d,DWORD PTR [rsi+0x8]
  0x00007facb1060c84: cmp    rax,r10
  0x00007facb1060c87: jne    0x00007facb1037960  ;   {runtime_call}
  0x00007facb1060c8d: xchg   ax,ax
[Verified Entry Point]
  0x00007facb1060c90: sub    rsp,0x18
  0x00007facb1060c97: mov    QWORD PTR [rsp+0x10],rbp  ;*synchronization entry
                                                ; - io.jaq.spsc.FFBuffer::poll@-1 (line 133)

nitsanw

public E poll() {
  final long offset = offset(head);
  final E[] lb = buffer;
  @SuppressWarnings("unchecked")
  final E e = (E) UnsafeAccess.UNSAFE.getObjectVolatile(lb, offset);
  if (null == e) {
     return null;
  }
  UnsafeAccess.UNSAFE.putOrderedObject(lb, offset, null);
  head++;

nitsanw

  # {method} 'poll' '()Ljava/lang/Object;' in 'io/jaq/spsc/FFBuffer' AFTER
  #           [sp+0x20]  (sp of caller)
  0x00007f885ca2ccc0: mov    r10d,DWORD PTR [rsi+0x8]
  0x00007f885ca2ccc4: cmp    rax,r10
  0x00007f885ca2ccc7: jne    0x00007f885ca03960  ;   {runtime_call}
  0x00007f885ca2cccd: xchg   ax,ax
[Verified Entry Point]
  0x00007f885ca2ccd0: sub    rsp,0x18
  0x00007f885ca2ccd7: mov    QWORD PTR [rsp+0x10],rbp  ;*synchronization entry
                                                ; - io.jaq.spsc.FFBuffer::poll@-1 (line 133)

nitsanw

/**
 * Allocates a new block of native memory, of the given size in bytes.The
 * contents of the memory are uninitialized; they will generally be
 * garbage.The resulting native pointer will never be zero, and will be
 * aligned for all value types.Dispose of this memory by calling {@link
 * #freeMemory}, or resize it with {@link #reallocateMemory}.
 *
 * @throws IllegalArgumentException if the size is negative or too large
 * for the native size_t type
 *

nitsanw

class Foo{
  volatile Foo next;

  Foo getNextNext(){
    // Commented out code as reminder of silly bug
//    if (next != null) {
//      // This can still result in NPE, next can change between reads
//      return next.next;
//    }
    // This is how we do it!

nitsanw

  static final int REF_SIZE = ...;
  static final int OBJECT_ARRAY_BASE = UNSAFE.arrayBaseOffset((Object[].class);
  static final boolean USE_COMPRESSED_REFS = ...;
  static final int COMPRESSED_REF_SHIFT = ...;
  public static long addressOf(Object o) {
    return addressOf(o, REF_SIZE);
  }

  public static long addressOf(Object o, int oopSize) {
    Object[] array = new Object[1];

nitsanw

// Let Shipilev do all the heavy lifting!
import org.openjdk.jol.util.VMSupport;
...

  // Suddenly, I feel the urge to get an object address
  long address =  VMSupport.addressOf(anUnsuspectingObject);
  
  // Satisfied. I move on to never using that address...
...

nitsanw

public static long sizeOf(Object object) {
  Unsafe unsafe = getUnsafe();
  // Original : return unsafe.getAddress( normalize( unsafe.getInt(object, 4L) ) + 12L );
  // This is my elaborate breakdown of original one liner
  int addressOfKlassInObjectHeader = unsafe.getInt(object, 4L);
  long nativeAddressOfKlass = normalize(addressOfKlassInObjectHeader);
  long addressOfLayoutHelper = nativeAddressOfKlass + 12L;
  return unsafe.getAddress(addressOfLayoutHelper);
}

nitsanw

static Object shallowCopy(Object obj) {
  long size = sizeOf(obj);
  long start = toAddress(obj);
  long address = getUnsafe().allocateMemory(size);
  getUnsafe().copyMemory(start, address, size);
  return fromAddress(address);
}

static long toAddress(Object obj) {
  Object[] array = new Object[] {obj};

nitsanw

@Override
public boolean offer(final E e) {
  if (null == e) {
    throw new NullPointerException("Null is not a valid element");
  }
  final long currHeadCache = lvHeadCache(); // Must load volatile, may have changed by other producer
  long currentTail;
  do {
    currentTail = lvTail(); // Must load volatile, may have changed by other producer
    final long wrapPoint = currentTail - capacity;