slightly decrease thread contention by synchronizing once rather than "number quantiles + 1" times (#481)

Signed-off-by: Yaroslav Klymko <[email protected]>

Author: t3hnar

simpleclient/src/main/java/io/prometheus/client/CKMSQuantiles.java

@@ -87,7 +87,7 @@ public CKMSQuantiles(Quantile[] quantiles) {
      * 
      * @param value
      */
-    public synchronized void insert(double value) {
+    public void insert(double value) {
         buffer[bufferCount] = value;
         bufferCount++;
 
@@ -104,7 +104,7 @@ public synchronized void insert(double value) {
      *            Queried quantile, e.g. 0.50 or 0.99.
      * @return Estimated value at that quantile.
      */
-    public synchronized double get(double q) {
+    public double get(double q) {
         // clear the buffer
         insertBatch();
         compress();

simpleclient/src/main/java/io/prometheus/client/TimeWindowQuantiles.java

@@ -27,19 +27,19 @@ public TimeWindowQuantiles(Quantile[] quantiles, long maxAgeSeconds, int ageBuck
     this.durationBetweenRotatesMillis = TimeUnit.SECONDS.toMillis(maxAgeSeconds) / ageBuckets;
   }
 
-  public double get(double q) {
+  public synchronized double get(double q) {
     CKMSQuantiles currentBucket = rotate();
     return currentBucket.get(q);
   }
 
-  public void insert(double value) {
+  public synchronized void insert(double value) {
     rotate();
     for (CKMSQuantiles ckmsQuantiles : ringBuffer) {
       ckmsQuantiles.insert(value);
     }
   }
 
-  private synchronized CKMSQuantiles rotate() {
+  private CKMSQuantiles rotate() {
     long timeSinceLastRotateMillis = System.currentTimeMillis() - lastRotateTimestampMillis;
     while (timeSinceLastRotateMillis > durationBetweenRotatesMillis) {
       ringBuffer[currentBucket] = new CKMSQuantiles(quantiles);