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HDDS-15357. Fix MappedBufferManager WeakReference races #10351

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HDDS-15357. Fix MappedBufferManager WeakReference races #10351

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23 changes: 15 additions & 8 deletions ...ce/src/main/java/org/apache/hadoop/ozone/container/keyvalue/impl/MappedBufferManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@
import com.google.common.util.concurrent.Striped;
import java.lang.ref.WeakReference;
import java.nio.ByteBuffer;
import java.util.Map;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.Semaphore;
Expand Down Expand Up @@ -57,10 +58,14 @@ public boolean getQuota(int permits) {
CompletableFuture.runAsync(() -> {
int p = 0;
try {
for (String key : mappedBuffers.keySet()) {
ByteBuffer buf = mappedBuffers.get(key).get();
if (buf == null) {
mappedBuffers.remove(key);
// remove(key, value) only counts entries we observed cleared,
// so a concurrent put() that replaced the WeakReference is not
// miscounted as freed.
for (Map.Entry<String, WeakReference<ByteBuffer>> entry
: mappedBuffers.entrySet()) {
final WeakReference<ByteBuffer> ref = entry.getValue();
if (ref.get() == null
&& mappedBuffers.remove(entry.getKey(), ref)) {
p++;
}
}
Expand Down Expand Up @@ -93,14 +98,16 @@ public ByteBuffer computeIfAbsent(String file, long position, long size,
Lock fileLock = lock.get(key);
fileLock.lock();
try {
WeakReference<ByteBuffer> refer = mappedBuffers.get(key);
if (refer != null && refer.get() != null) {
// reuse the mapped buffer
// Hold a strong reference for the rest of this method so GC cannot
// clear the WeakReference between the null check and the return.
final WeakReference<ByteBuffer> refer = mappedBuffers.get(key);
final ByteBuffer cached = refer != null ? refer.get() : null;
if (cached != null) {
if (LOG.isDebugEnabled()) {
LOG.debug("find buffer for key {}", key);
}
releaseQuota(1);
return refer.get();
return cached;
}

ByteBuffer buffer = supplier.get();
Expand Down