Package zombie.core.Collections
Class ConcurrentAutoTable
java.lang.Object
zombie.core.Collections.ConcurrentAutoTable
- All Implemented Interfaces:
Serializable
- Direct Known Subclasses:
Counter
An auto-resizing table of
longs
, supporting low-contention CAS
operations. Updates are done with CAS's to no particular table element.
The intent is to support highly scalable counters, r/w locks, and other
structures where the updates are associative, loss-free (no-brainer), and
otherwise happen at such a high volume that the cache contention for
CAS'ing a single word is unacceptable.
This API is overkill for simple counters (e.g. no need for the 'mask') and is untested as an API for making a scalable r/w lock and so is likely to change!
- Since:
- 1.5
- See Also:
-
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionvoid
add
(long x) Add the given value to current counter value.void
add(long)
with -1long
A cheaperget()
.long
get()
Current value of the counter.void
add(long)
with +1int
Return the internal counter striping factor.int
intValue()
Same asget()
, included for completeness.long
Same asget()
, included for completeness.void
print()
A more verbose print thantoString()
, showing internal structure.void
set
(long x) Atomically set the sum of the striped counters to specified value.toString()
Return the counter'slong
value converted to a string.
-
Constructor Details
-
ConcurrentAutoTable
public ConcurrentAutoTable()
-
-
Method Details
-
add
public void add(long x) Add the given value to current counter value. Concurrent updates will not be lost, but addAndGet or getAndAdd are not implemented because the total counter value (i.e.,get()
) is not atomically updated. Updates are striped across an array of counters to avoid cache contention and has been tested with performance scaling linearly up to 768 CPUs. -
decrement
public void decrement()add(long)
with -1 -
increment
public void increment()add(long)
with +1 -
set
public void set(long x) Atomically set the sum of the striped counters to specified value. Rather more expensive than a simple store, in order to remain atomic. -
get
public long get()Current value of the counter. Since other threads are updating furiously the value is only approximate, but it includes all counts made by the current thread. Requires a pass over the internally striped counters. -
intValue
public int intValue()Same asget()
, included for completeness. -
longValue
public long longValue()Same asget()
, included for completeness. -
estimate_get
public long estimate_get()A cheaperget()
. Updated only once/millisecond, but as fast as a simple load instruction when not updating. -
toString
Return the counter'slong
value converted to a string. -
print
public void print()A more verbose print thantoString()
, showing internal structure. Useful for debugging. -
internal_size
public int internal_size()Return the internal counter striping factor. Useful for diagnosing performance problems.
-