package org.argeo.api.uuid;
+import static java.lang.System.Logger.Level.DEBUG;
+import static java.lang.System.Logger.Level.WARNING;
+
+import java.lang.System.Logger;
import java.security.SecureRandom;
import java.time.Clock;
import java.time.Duration;
import java.time.Instant;
import java.util.Objects;
+import java.util.Set;
+import java.util.WeakHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
/**
* A simple base implementation of {@link TimeUuidState}, which maintains
* different clock sequences for each thread.
*/
public class ConcurrentTimeUuidState implements TimeUuidState {
-// public final static ThreadLocal<Boolean> isTimeUuidThread = new ThreadLocal<>() {
-//
-// @Override
-// protected Boolean initialValue() {
-// return false;
-// }
-// };
+ private final static Logger logger = System.getLogger(ConcurrentTimeUuidState.class.getName());
/** The maximum possible value of the clocksequence. */
private final static int MAX_CLOCKSEQUENCE = 16384;
- private final ThreadLocal<Holder> holder;
+ private final ClockSequenceProvider clockSequenceProvider;
+ private final ThreadLocal<ConcurrentTimeUuidState.Holder> currentHolder;
private final Instant startInstant;
/** A start timestamp to which {@link System#nanoTime()}/100 can be added. */
private final Clock clock;
private final boolean useClockForMeasurement;
- private final SecureRandom secureRandom;
-
public ConcurrentTimeUuidState(SecureRandom secureRandom, Clock clock) {
useClockForMeasurement = clock != null;
this.clock = clock != null ? clock : Clock.systemUTC();
Objects.requireNonNull(secureRandom);
- this.secureRandom = secureRandom;
// compute the start reference
startInstant = Instant.now(this.clock);
Duration duration = Duration.between(TimeUuidState.GREGORIAN_START, startInstant);
startTimeStamp = durationToUuidTimestamp(duration) - nowVm;
+ clockSequenceProvider = new ClockSequenceProvider(secureRandom);
+
// initalise a state per thread
- holder = new ThreadLocal<>() {
+ currentHolder = new ThreadLocal<>() {
@Override
- protected Holder initialValue() {
- Holder value = new Holder();
+ protected ConcurrentTimeUuidState.Holder initialValue() {
+ ConcurrentTimeUuidState.Holder value = new ConcurrentTimeUuidState.Holder();
+ value.threadId = Thread.currentThread().getId();
value.lastTimestamp = startTimeStamp;
- value.clockSequence = newClockSequence();
-// isTimeUuidThread.set(true);
+ clockSequenceProvider.newClockSequence(value);
return value;
}
};
*/
public long useTimestamp() {
+ Holder holder = currentHolder.get();
+ if (holder.clockSequence < 0) {
+ clockSequenceProvider.newClockSequence(holder);
+ }
- long previousTimestamp = holder.get().lastTimestamp;
+ long previousTimestamp = holder.lastTimestamp;
long now = computeNow();
// rare case where we are sooner
// (e.g. if system time has changed in between and we use the clock)
if (previousTimestamp > now) {
- long newClockSequence = newClockSequence();
- for (int i = 0; i < 64; i++) {
- if (newClockSequence != holder.get().clockSequence)
- break;
- newClockSequence = newClockSequence();
- }
- if (newClockSequence != holder.get().clockSequence)
- throw new IllegalStateException("Cannot change clock sequence");
- holder.get().clockSequence = newClockSequence;
+ clockSequenceProvider.newClockSequence(holder);
}
// very unlikely case where it took less than 100ns between both
now = computeNow();
assert previousTimestamp != now;
}
- holder.get().lastTimestamp = now;
+ holder.lastTimestamp = now;
return now;
}
- protected long computeNow() {
+ private long computeNow() {
if (useClockForMeasurement) {
Duration duration = Duration.between(TimeUuidState.GREGORIAN_START, Instant.now(clock));
return durationToUuidTimestamp(duration);
return System.nanoTime() / 100;
}
- protected long durationToUuidTimestamp(Duration duration) {
+ private long durationToUuidTimestamp(Duration duration) {
return (duration.getSeconds() * 10000000 + duration.getNano() / 100);
}
- /*
- * STATE OPERATIONS
- */
+ @Override
+ public long getClockSequence() {
+ return (long) currentHolder.get().clockSequence;
+ }
+
+ private static class Holder {
+ private long lastTimestamp;
+ private int clockSequence;
+ private long threadId;
+
+ @Override
+ public boolean equals(Object obj) {
+ boolean isItself = this == obj;
+ if (!isItself && clockSequence == ((Holder) obj).clockSequence)
+ throw new IllegalStateException("There is another holder with the same clockSequence " + clockSequence);
+ return isItself;
+ }
+
+ private synchronized void setClockSequence(int clockSequence) {
+ this.clockSequence = clockSequence;
+ }
+
+ @Override
+ public String toString() {
+ return "Holder " + clockSequence + ", threadId=" + threadId + ", lastTimestamp=" + lastTimestamp;
+ }
- protected long newClockSequence() {
- return secureRandom.nextInt(ConcurrentTimeUuidState.MAX_CLOCKSEQUENCE);
}
- /*
- * ACCESSORS
- */
+ private static class ClockSequenceProvider {
+ private int rangeSize = 256;
+ private volatile int min;
+ private volatile int max;
+ private final AtomicInteger counter = new AtomicInteger(-1);
-// @Override
-// public byte[] getNodeId() {
-// byte[] arr = new byte[6];
-// System.arraycopy(holder.get().nodeId, 0, arr, 0, 6);
-// return arr;
-// }
+ private final SecureRandom secureRandom;
+
+ private final WeakHashMap<Holder, Integer> activeHolders = new WeakHashMap<>();
+
+ ClockSequenceProvider(SecureRandom secureRandom) {
+ this.secureRandom = secureRandom;
+ reset();
+ }
+
+ synchronized void reset() {
+ int min = secureRandom.nextInt(ConcurrentTimeUuidState.MAX_CLOCKSEQUENCE);
+ int max = min + rangeSize;
+ if (min >= max)
+ throw new IllegalArgumentException("Minimum " + min + " is bigger than maximum " + max);
+ if (min < 0 || min > MAX_CLOCKSEQUENCE)
+ throw new IllegalArgumentException("Minimum " + min + " is not valid");
+ if (max < 0 || max > MAX_CLOCKSEQUENCE)
+ throw new IllegalArgumentException("Maximum " + max + " is not valid");
+ this.min = min;
+ this.max = max;
+
+ Set<Holder> active = activeHolders.keySet();
+ int activeCount = active.size();
+ if (activeCount > getRangeSize())
+ throw new IllegalStateException(
+ "There are too many holders for range [" + min + "," + max + "] : " + activeCount);
+ // reset the counter
+ counter.set(min);
+ for (Holder holder : active) {
+ // save old clocksequence?
+ newClockSequence(holder);
+ }
+ }
+
+ private synchronized int getRangeSize() {
+ return rangeSize;
+ }
+
+ private synchronized void newClockSequence(Holder holder) {
+// int activeCount = activeHolders.size();
+ while (activeHolders.size() > rangeSize) {
+// throw new IllegalStateException(
+// "There are too many holders for range [" + min + "," + max + "] : " + activeCount);
+ // remove oldest
+ long oldestTimeStamp = -1;
+ Holder holderToRemove = null;
+ holders: for (Holder h : activeHolders.keySet()) {
+ if (h == holder)// skip the caller
+ continue holders;
+
+ if (oldestTimeStamp < 0) {
+ oldestTimeStamp = h.lastTimestamp;
+ holderToRemove = h;
+ }
+ if (h.lastTimestamp <= oldestTimeStamp) {
+ oldestTimeStamp = h.lastTimestamp;
+ holderToRemove = h;
+ }
+
+ }
+ assert holderToRemove != null;
+ long oldClockSequence = holderToRemove.clockSequence;
+ holderToRemove.clockSequence = -1;
+ activeHolders.remove(holderToRemove);
+ if (logger.isLoggable(WARNING))
+ logger.log(WARNING, "Removed " + holderToRemove + ", oldClockSequence=" + oldClockSequence);
+ }
+
+ int newClockSequence = -1;
+ int tryCount = 0;// an explicit exit condition
+ do {
+ tryCount++;
+ if (tryCount >= rangeSize)
+ throw new IllegalStateException("No more clock sequence available");
+
+ newClockSequence = counter.incrementAndGet();
+ assert newClockSequence >= 0 : "Clock sequence cannot be negative";
+ if (newClockSequence > max) {
+ // reset counter
+ newClockSequence = min;
+ counter.set(newClockSequence);
+ }
+ } while (activeHolders.containsValue(newClockSequence));
+ // TODO use an iterator to check the values
+ holder.setClockSequence(newClockSequence);
+ activeHolders.put(holder, newClockSequence);
+ if (logger.isLoggable(DEBUG))
+ logger.log(DEBUG,
+ "New clocksequence " + newClockSequence + " for thread " + Thread.currentThread().getId());
+ }
- @Override
- public long getClockSequence() {
- return holder.get().clockSequence;
}
+
}
projects / lgpl / argeo-commons.git / commitdiff