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Fixed rare race condition in ActiveSectionTracker, occured more frequently with high core systems. This is hopefully the last concurrency bug in the tracker

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This commit is contained in:
mcrcortex
2025-09-11 01:32:24 +10:00
parent 81741974bb
commit 9f4282e37b
2 changed files with 50 additions and 16 deletions
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56
src/main/java/me/cortex/voxy/common/world/ActiveSectionTracker.java
View File

@@ -113,6 +113,10 @@ public class ActiveSectionTracker {
long stamp = this.lruLock.writeLock();
section = this.lruSecondaryCache.remove(key);
this.lruLock.unlockWrite(stamp);
if (section != null) {
section.primeForReuse();
section.acquire(1);
}
lock.unlockRead(stamp2);
} else {
VolatileHolder.PRE_ACQUIRE_COUNT.getAndAdd(holder, 1);
@@ -142,11 +146,10 @@ public class ActiveSectionTracker {
//We need to set the data to air as it is undefined state
Arrays.fill(section.data, 0);
}
} else {
section.primeForReuse();
section.acquire(1);
}
int preAcquireCount = (int) VolatileHolder.PRE_ACQUIRE_COUNT.getAndSet(holder, 0);
section.acquire(preAcquireCount+1);//pre acquire amount
section.acquire(preAcquireCount);//pre acquire amount
VolatileHolder.POST_ACQUIRE_COUNT.set(holder, preAcquireCount);
//TODO: mark if the section was loaded null
@@ -223,7 +226,7 @@ public class ActiveSectionTracker {
var cached = cache.remove(section.key);
var obj = cached.obj;
if (obj == null) {
throw new IllegalStateException("This should be impossible: " + WorldEngine.pprintPos(section.key));
throw new IllegalStateException("This should be impossible: " + WorldEngine.pprintPos(section.key) + " secObj: " + System.identityHashCode(section));
}
if (obj != section) {
throw new IllegalStateException("Removed section not the same as the referenced section in the cache: cached: " + obj + " got: " + section + " A: " + WorldSection.ATOMIC_STATE_HANDLE.get(obj) + " B: " +WorldSection.ATOMIC_STATE_HANDLE.get(section));
@@ -235,6 +238,7 @@ public class ActiveSectionTracker {
WorldSection aa = null;
if (sec != null) {
long stamp2 = this.lruLock.writeLock();
lock.unlockWrite(stamp);
WorldSection a = this.lruSecondaryCache.put(section.key, section);
if (a != null) {
throw new IllegalStateException("duplicate sections in cache is impossible");
@@ -245,9 +249,10 @@ public class ActiveSectionTracker {
}
this.lruLock.unlockWrite(stamp2);
} else {
lock.unlockWrite(stamp);
}
lock.unlockWrite(stamp);
if (aa != null) {
aa._releaseArray();
@@ -276,16 +281,45 @@ public class ActiveSectionTracker {
return this.lruSecondaryCache.size();
}
public static void main(String[] args) {
var tracker = new ActiveSectionTracker(1, a->0, 1<<10);
public static void main(String[] args) throws InterruptedException {
var tracker = new ActiveSectionTracker(6, a->0, 2<<10);
var bean = tracker.acquire(0, 0, 0, 9, false);
var bean2 = tracker.acquire(1, 0, 0, 0, false);
System.out.println("Target obj:" + System.identityHashCode(bean2));
bean2.release();
Thread[] ts = new Thread[10];
for (int i = 0; i < ts.length;i++) {
int tid = i;
ts[i] = new Thread(()->{
try {
for (int j = 0; j < 5000; j++) {
if (true) {
var section = tracker.acquire(0, 0, 0, 0, false);
section.acquire();
var section2 = tracker.acquire(0,0,0,0, false);
var section2 = tracker.acquire(1, 0, 0, 0, false);
section.release();
section.release();
section = tracker.acquire(0,0,0,0, false);
section.release();
section2.release();
}
if (true) {
var section = tracker.acquire(0, 0, 0, 0, false);
var section2 = tracker.acquire(1, 0, 0, 0, false);
section2.release();
section.release();
}
if (true) {
tracker.acquire(1, 0, 0, 0, false).release();
}
}
} catch (Exception e) {
throw new RuntimeException("Thread " + tid, e);
}
});
ts[i].start();
}
for (var t : ts) {
t.join();
}
}
}

2
src/main/java/me/cortex/voxy/common/world/WorldSection.java
View File

@@ -122,7 +122,7 @@ public final class WorldSection {
public int acquire(int count) {
int state = ((int) ATOMIC_STATE_HANDLE.getAndAdd(this, count<<1)) + (count<<1);
if ((state & 1) == 0) {
throw new IllegalStateException("Tried to acquire unloaded section: " + WorldEngine.pprintPos(this.key));
throw new IllegalStateException("Tried to acquire unloaded section: " + WorldEngine.pprintPos(this.key) + " obj: " + System.identityHashCode(this));
}
return state>>1;
}