はい、これは私も遭遇した一般的な問題です。いくつかの回避策があります (説明されているように手動で設定するなど)。
- MDC を一貫して設定します。
- MDC が間違っているがそれがわからないという暗黙のバグを回避します。と
- スレッド プールの使用方法の変更を最小限に抑えます (例: Everywhere でのサブクラス化
Callable、MyCallableまたは同様の醜さ)。
これら 3 つのニーズを満たす、私が使用するソリューションを次に示します。コードは自明であるべきです。
MoreExecutors.listeningDecorator()(補足として、Guava のを使用する場合、このエグゼキュータを作成して Guava の に供給することができますListanableFuture。)
import org.slf4j.MDC;
import java.util.Map;
import java.util.concurrent.*;
/**
* A SLF4J MDC-compatible {@link ThreadPoolExecutor}.
* <p/>
* In general, MDC is used to store diagnostic information (e.g. a user's session id) in per-thread variables, to facilitate
* logging. However, although MDC data is passed to thread children, this doesn't work when threads are reused in a
* thread pool. This is a drop-in replacement for {@link ThreadPoolExecutor} sets MDC data before each task appropriately.
* <p/>
* Created by jlevy.
* Date: 6/14/13
*/
public class MdcThreadPoolExecutor extends ThreadPoolExecutor {
final private boolean useFixedContext;
final private Map<String, Object> fixedContext;
/**
* Pool where task threads take MDC from the submitting thread.
*/
public static MdcThreadPoolExecutor newWithInheritedMdc(int corePoolSize, int maximumPoolSize, long keepAliveTime,
TimeUnit unit, BlockingQueue<Runnable> workQueue) {
return new MdcThreadPoolExecutor(null, corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
/**
* Pool where task threads take fixed MDC from the thread that creates the pool.
*/
@SuppressWarnings("unchecked")
public static MdcThreadPoolExecutor newWithCurrentMdc(int corePoolSize, int maximumPoolSize, long keepAliveTime,
TimeUnit unit, BlockingQueue<Runnable> workQueue) {
return new MdcThreadPoolExecutor(MDC.getCopyOfContextMap(), corePoolSize, maximumPoolSize, keepAliveTime, unit,
workQueue);
}
/**
* Pool where task threads always have a specified, fixed MDC.
*/
public static MdcThreadPoolExecutor newWithFixedMdc(Map<String, Object> fixedContext, int corePoolSize,
int maximumPoolSize, long keepAliveTime, TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
return new MdcThreadPoolExecutor(fixedContext, corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
private MdcThreadPoolExecutor(Map<String, Object> fixedContext, int corePoolSize, int maximumPoolSize,
long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
this.fixedContext = fixedContext;
useFixedContext = (fixedContext != null);
}
@SuppressWarnings("unchecked")
private Map<String, Object> getContextForTask() {
return useFixedContext ? fixedContext : MDC.getCopyOfContextMap();
}
/**
* All executions will have MDC injected. {@code ThreadPoolExecutor}'s submission methods ({@code submit()} etc.)
* all delegate to this.
*/
@Override
public void execute(Runnable command) {
super.execute(wrap(command, getContextForTask()));
}
public static Runnable wrap(final Runnable runnable, final Map<String, Object> context) {
return new Runnable() {
@Override
public void run() {
Map previous = MDC.getCopyOfContextMap();
if (context == null) {
MDC.clear();
} else {
MDC.setContextMap(context);
}
try {
runnable.run();
} finally {
if (previous == null) {
MDC.clear();
} else {
MDC.setContextMap(previous);
}
}
}
};
}
}