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Mock reporter for testing reporters #85

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Mock reporter for testing reporters #85

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dinomite
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A simple reporter mock that allows access to the metrics registry contained therein.

@dinomite
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'ang on a minute—I've got a better idea.

@dinomite dinomite closed this Sep 27, 2011
carterkozak added a commit to carterkozak/metrics that referenced this pull request Oct 6, 2020
@carterkozak
optimize rescaleIfNeeded below the 35b inline threshold
10f4c02 
This makes the check more likely to be optimized without forcing
analysis of the less common doRescale path.

Before:
```
private LockFreeExponentiallyDecayingReservoir$State
rescaleIfNeeded(long)
     0: aload_0
     1: getfield        dropwizard#56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
     4: astore_3
     5: aload_3
     6: invokestatic    dropwizard#81  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.access$600:(Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)J
     9: lstore          4
    11: lload_1
    12: lload           4
    14: lsub
    15: aload_0
    16: getfield        dropwizard#36  // Field rescaleThresholdNanos:J
    19: lcmp
    20: iflt            51
    23: aload_3
    24: lload_1
    25: invokevirtual   dropwizard#85  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.rescale:(J)Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    28: astore          6
    30: getstatic       dropwizard#88  // Field
stateUpdater:Ljava/util/concurrent/atomic/AtomicReferenceFieldUpdater;
    33: aload_0
    34: aload_3
    35: aload           6
    37: invokevirtual   dropwizard#92  // Method
java/util/concurrent/atomic/AtomicReferenceFieldUpdater.compareAndSet:(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Z
    40: ifeq            46
    43: aload           6
    45: areturn
    46: aload_0
    47: getfield        dropwizard#56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    50: areturn
    51: aload_3
    52: areturn
```

After:
```
private LockFreeExponentiallyDecayingReservoir$State
rescaleIfNeeded(long)
     0: aload_0
     1: getfield        dropwizard#56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
     4: astore_3
     5: lload_1
     6: aload_3
     7: invokestatic    dropwizard#81  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.access$600:(Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)J
    10: lsub
    11: aload_0
    12: getfield        dropwizard#36  // Field rescaleThresholdNanos:J
    15: lcmp
    16: iflt            26
    19: aload_0
    20: lload_1
    21: aload_3
    22: invokespecial   dropwizard#85  // Method
doRescale:(JLcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    25: areturn
    26: aload_3
    27: areturn
```
joschi pushed a commit that referenced this pull request Oct 21, 2020
@carterkozak
Implement LockFreeExponentiallyDecayingReservoir (#1656)
53419ff 
* Implement LockFreeExponentiallyDecayingReservoir

This implementation has several advantages over the existing
ExponentiallyDecayingReservoir:
* It exclusively uses the precise system clock (nanotime/clock.tick)
  instead of a combination of nanotime and currentTimeMillis so it's
  not vulnerable to unexpected NTP clock jumps.
* Lock free for substantially better performance under concurrent
  load[1] and improved performance in uncontended use[2]
* Allows the rescale threshold to be configured programatically.

Potential trade-offs:
* Updates which occur concurrently with rescaling may be discarded if
  the orphaned state node is updated after rescale has replaced it.
* In the worst case, all concurrent threads updating the reservoir may
  attempt to rescale rather than a single thread holding an exclusive
  write lock. It's expected that the configuration is set such that
  rescaling is substantially less common than updating at peak load.

[1] substantially better performance under concurrent load
32 concurrent update threads
```
Benchmark                                 (reservoirType)  Mode  Cnt
Score      Error  Units
ReservoirBenchmarks.updateReservoir            EXPO_DECAY  avgt    5 8235.861 ± 1306.404  ns/op
ReservoirBenchmarks.updateReservoir  LOCK_FREE_EXPO_DECAY  avgt    5 758.315 ±   36.916  ns/op
```

[2] improved performance in uncontended use
1 benchmark thread
```
Benchmark                                 (reservoirType)  Mode  Cnt
Score    Error  Units
ReservoirBenchmarks.updateReservoir            EXPO_DECAY  avgt    5 92.845 ± 36.478  ns/op
ReservoirBenchmarks.updateReservoir  LOCK_FREE_EXPO_DECAY  avgt    5 49.168 ±  1.033  ns/op
```

* Precompute alpha at nanosecond scale

Avoid expensive division operations on each rescale and update

* Optimize weightedsample allocations on update

* Refactor `update` to avoid isEmpty

```
Benchmark                                 (reservoirType)  Mode  Cnt     Score      Error  Units
ReservoirBenchmarks.updateReservoir            EXPO_DECAY  avgt    5  8365.308 ± 1880.683  ns/op
ReservoirBenchmarks.updateReservoir  LOCK_FREE_EXPO_DECAY  avgt    5    73.966 ±    5.305  ns/op
```

* Code review from @spkrka

* remove unnecessary validation

* readable decimals

* require positive size

* optimize rescaleIfNeeded below the 35b inline threshold

This makes the check more likely to be optimized without forcing
analysis of the less common doRescale path.

Before:
```
private LockFreeExponentiallyDecayingReservoir$State
rescaleIfNeeded(long)
     0: aload_0
     1: getfield        #56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
     4: astore_3
     5: aload_3
     6: invokestatic    #81  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.access$600:(Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)J
     9: lstore          4
    11: lload_1
    12: lload           4
    14: lsub
    15: aload_0
    16: getfield        #36  // Field rescaleThresholdNanos:J
    19: lcmp
    20: iflt            51
    23: aload_3
    24: lload_1
    25: invokevirtual   #85  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.rescale:(J)Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    28: astore          6
    30: getstatic       #88  // Field
stateUpdater:Ljava/util/concurrent/atomic/AtomicReferenceFieldUpdater;
    33: aload_0
    34: aload_3
    35: aload           6
    37: invokevirtual   #92  // Method
java/util/concurrent/atomic/AtomicReferenceFieldUpdater.compareAndSet:(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Z
    40: ifeq            46
    43: aload           6
    45: areturn
    46: aload_0
    47: getfield        #56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    50: areturn
    51: aload_3
    52: areturn
```

After:
```
private LockFreeExponentiallyDecayingReservoir$State
rescaleIfNeeded(long)
     0: aload_0
     1: getfield        #56  // Field
state:Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
     4: astore_3
     5: lload_1
     6: aload_3
     7: invokestatic    #81  // Method
com/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State.access$600:(Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)J
    10: lsub
    11: aload_0
    12: getfield        #36  // Field rescaleThresholdNanos:J
    15: lcmp
    16: iflt            26
    19: aload_0
    20: lload_1
    21: aload_3
    22: invokespecial   #85  // Method
doRescale:(JLcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;)Lcom/codahale/metrics/LockFreeExponentiallyDecayingReservoir$State;
    25: areturn
    26: aload_3
    27: areturn
```

* Avoid incrementing count when the value has reached size.

```
Benchmark                                 (reservoirType)  Mode  Cnt     Score      Error  Units
ReservoirBenchmarks.updateReservoir            EXPO_DECAY  avgt    5  8309.300 ± 1900.398  ns/op
ReservoirBenchmarks.updateReservoir  LOCK_FREE_EXPO_DECAY  avgt    5    70.028 ±    0.887  ns/op
```

* rescale cannot exceed size elements

* line length

* requireNonNull validation

* Include LockFreeExponentiallyDecayingReservoir in ReservoirBenchmark

Results with 32 concurrent threads on a 14c/28t Xeon W-2175
```
Benchmark                                                      Mode  Cnt   Score    Error  Units
ReservoirBenchmark.perfExponentiallyDecayingReservoir          avgt    4   8.817 ±  0.310  us/op
ReservoirBenchmark.perfLockFreeExponentiallyDecayingReservoir  avgt    4   0.076 ±  0.002  us/op
ReservoirBenchmark.perfSlidingTimeWindowArrayReservoir         avgt    4  14.890 ±  0.489  us/op
ReservoirBenchmark.perfSlidingTimeWindowReservoir              avgt    4  39.066 ± 27.583  us/op
ReservoirBenchmark.perfSlidingWindowReservoir                  avgt    4   4.257 ±  0.187  us/op
ReservoirBenchmark.perfUniformReservoir                        avgt    4   0.704 ±  0.040  us/op
```

Thanks @carterkozak, @schlosna, and @spkrka!
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@dinomite