我在处理软引用和弱引用时遇到了问题。代码中有一个开关，可以在软引用和弱引用之间切换全部逻辑。而且尽管使用弱引用似乎一切正常，但是我不断地遇到OutOfMemoryError（内存溢出错误）的问题。这种情况在MacOSX上的JDK7和JDK6以及Debian上的IcedTea6中都会发生。然而，我发现使用带有G1收集器的JDK7与软引用一起使用的设置可以解决问题，其他所有尝试（串行/并行GC、-client/-server等）都会失败并抛出异常。
代码有点大，但我已经尽可能缩小范围来保留问题。我在顶部留下了大量注释，在其中更详细地描述了如何重现此问题。
/*
*
* Leakling.java
*
*
* Issue:
*
*
* This code throws OutOfMemoryError when using soft references, whereas weak references
* work ok. Moreover, with JDK7 G1 garbage collector soft references work as well. Other
* collectors seem to fail. Code was tested with MacOSX 10.8.2 JDKs 1.7.0_10-b18 and
* 1.6.0_37-b06-434-11M3909, with Debian 6.0 IcedTea6 1.8.13.
* Various command line options including -Xmx, -client/-server, -XX:+UseParallelOldGC,
* -XX:+UseSerialGC were tested.
*
*
* Examples:
*
*
* 1. Default options, weak references, this works, counters go up and down,
* but everything keeps going just as expected:
*
* java -Xmx50m Leakling \
* --loop-delay=10 --min-chunk-size=1000 --max-chunk-size=100000 --use-soft-references=false
*
*
* 2. Default options, soft references, this eventually throws the exception:
*
* java -Xmx50m Leakling \
* --loop-delay=10 --min-chunk-size=1000 --max-chunk-size=100000 --use-soft-references=true
*
*
* 3. G1 collector (IcedTea6 doesn't support it), weak references, this works, but it did anyway:
*
* java -XX:+UseG1GC -Xmx50m Leakling \
* --loop-delay=10 --min-chunk-size=1000 --max-chunk-size=100000 --use-soft-references=false
*
*
* 4. G1 collector, soft references, this works with JDK7.
* JDK6 seems to just stop after having hit memory limit (with no message whatsoever).
*
* java -XX:+UseG1GC -Xmx50m Leakling \
* --loop-delay=10 --min-chunk-size=1000 --max-chunk-size=100000 --use-soft-references=true
*
*
* jarek, 02.01.2013
*
*
*/
import java.lang.ref.*;
import java.util.*;
public class Leakling {
private static final String TAG = "memory-chunk-";
class Chunk {
final String name;
final int size;
final private byte[] mem;
Chunk(String name, int minSize, int maxSize, Random randomizer) {
int currSize = minSize;
if (maxSize > minSize) {
currSize += randomizer.nextInt(maxSize - minSize + 1);
}
this.size = currSize;
this.mem = new byte[currSize];
this.name = name;
log(this + " has been created (" + currSize + " bytes)");
}
@Override
public void finalize() throws Throwable {
log(this + " is finalizing");
}
@Override
public String toString() {
return name + " of " + getReadableMemorySize(size);
}
}
class WeakChunk extends WeakReference<Chunk> {
final String name;
public WeakChunk(Chunk chunk, ReferenceQueue<Chunk> queue) {
super(chunk, queue);
this.name = chunk.name;
}
@Override
public String toString() {
return "weak reference of " + name + " is " + ((get() == null) ? "null" : "alive");
}
}
class SoftChunk extends SoftReference<Chunk> {
final String name;
public SoftChunk(Chunk chunk, ReferenceQueue<Chunk> queue) {
super(chunk, queue);
this.name = chunk.name;
}
@Override
public String toString() {
return "soft reference of " + name + " is " + ((get() == null) ? "null" : "alive");
}
}
// Logging as implemented here gives extra timing info (secs.milis starting from the initialization).
private final long start = System.currentTimeMillis();
private final Formatter formatter = new Formatter(System.err);
private final String formatString = "%1$d.%2$03d %3$s\n";
// I found this be better synchronized...
synchronized void log(Object o) {
long curr = System.currentTimeMillis();
long diff = curr - start;
formatter.format(formatString, (int) (diff / 1000), (int) (diff % 1000), o.toString());
}
private final ArrayList<Chunk> allChunks = new ArrayList<Chunk>();
private final ReferenceQueue<Chunk> softReferences = new ReferenceQueue<Chunk>();
private final ReferenceQueue<Chunk> weakReferences = new ReferenceQueue<Chunk>();
private final HashSet<Reference<Chunk>> allReferences = new HashSet<Reference<Chunk>>();
private final Random randomizer = new Random();
private int loopDelay = 200;
private int minChunkSize = 100;
private int maxChunkSize = 1000;
private int chunkCounter = 0;
private boolean useSoftReferences = false;
private long minMemory = 10 * 1024 * 1024; // Default range is 10-30MB
private long maxMemory = 3 * minMemory;
private long usedMemory = 0;
private String getReadableMemorySize(long size) {
if (size >= 1024 * 1024) {
return (float) (Math.round((((float) size) / 1024f / 1024f) * 10f)) / 10f + "MB";
}
if (size >= 1024) {
return (float) (Math.round((((float) size) / 1024f) * 10f)) / 10f + "kB";
} else if (size > 0) {
return size + "B";
} else {
return "0";
}
}
private void allocMem() {
Chunk chunk = new Chunk(TAG + chunkCounter++, minChunkSize, maxChunkSize, randomizer);
allChunks.add(chunk);
Reference ref = useSoftReferences
? (new SoftChunk(chunk, softReferences)) : (new WeakChunk(chunk, weakReferences));
allReferences.add(ref);
log(ref);
usedMemory += chunk.size;
}
private void freeMem() {
if (allChunks.size() < 1) {
return;
}
int i = randomizer.nextInt(allChunks.size());
Chunk chunk = allChunks.get(i);
log("freeing " + chunk);
usedMemory -= chunk.size;
allChunks.remove(i);
}
private int statMem() throws Exception {
for (Reference ref; (ref = softReferences.poll()) != null;) {
log(ref);
allReferences.remove(ref);
}
for (Reference ref; (ref = weakReferences.poll()) != null;) {
log(ref);
allReferences.remove(ref);
}
int weakRefs = 0;
int softRefs = 0;
for (Iterator<Reference<Chunk>> i = allReferences.iterator(); i.hasNext();) {
Reference<Chunk> ref = i.next();
if (ref.get() == null) {
continue;
}
if (ref instanceof WeakChunk) {
weakRefs++;
}
if (ref instanceof SoftChunk) {
softRefs++;
}
}
log(allChunks.size() + " chunks, "
+ softRefs + " soft refs, "
+ weakRefs + " weak refs, "
+ getReadableMemorySize(usedMemory) + " used, "
+ getReadableMemorySize(Runtime.getRuntime().freeMemory()) + " free, "
+ getReadableMemorySize(Runtime.getRuntime().totalMemory()) + " total, "
+ getReadableMemorySize(Runtime.getRuntime().maxMemory()) + " max");
if (loopDelay > 1) {
Thread.sleep(loopDelay);
}
return (int)((100 * usedMemory) / maxMemory); // Return % of maxMemory being used.
}
public Leakling(String[] args) throws Exception {
for (String arg : args) {
if (arg.startsWith("--min-memory=")) {
minMemory = Long.parseLong(arg.substring("--min-memory=".length()));
} else if (arg.startsWith("--max-memory=")) {
maxMemory = Long.parseLong(arg.substring("--max-memory=".length()));
} else if (arg.startsWith("--min-chunk-size=")) {
minChunkSize = Integer.parseInt(arg.substring("--min-chunk-size=".length()));
} else if (arg.startsWith("--max-chunk-size=")) {
maxChunkSize = Integer.parseInt(arg.substring("--max-chunk-size=".length()));
} else if (arg.startsWith("--loop-delay=")) {
loopDelay = Integer.parseInt(arg.substring("--loop-delay=".length()));
} else if (arg.startsWith("--use-soft-references=")) {
useSoftReferences = Boolean.parseBoolean(arg.substring("--use-soft-references=".length()));
} else {
throw new Exception("Unknown command line option...");
}
}
}
public void run() throws Exception {
log("Mem test started...");
while(true) {
log("going up...");
do {// First loop allocates memory up to the given limit in a pseudo-random fashion.
// Randomized rate of allocations/frees is about 4:1 as per the 10>=8 condition.
if (randomizer.nextInt(10) >= 8) {
freeMem();
} else {
allocMem();
}
} while (statMem() < 90); // Repeat until 90% of the given mem limit is hit...
log("going down...");
do {// Now do the reverse. Frees are four times more likely than allocations are.
if (randomizer.nextInt(10) < 8) {
freeMem();
} else {
allocMem();
}
} while (usedMemory > minMemory);
}
}
public static void main(String[] args) throws Exception {
(new Leakling(args)).run();
}
}
- OOME 附带的消息是什么？
- 你不能指望别人查看整个代码。你应该将其编辑为精华并在此处发布，而不是使用 pastebin。
- Enno Shioji// Now do the reverse. Frees are four times more likely than allocations are.循环不是有问题吗？如果你一直得到 8、9、10，它不会一直分配内存吗？ - jn1kk