英文:
Is there a good way to add FutureLocal.java to custom Future.java extending CompletableFuture? (example code below)
问题
我有以下代码，它在调用super.thenCompose时返回一个CompletableFuture，而不是我自定义的Custom Future.java，这在关键时刻有点接近。我试图复制Twitter的Scala Futures，它们具有以下功能：
- 能够添加类似Twitter Scala Futures的取消链接。
- 可以在thenApply和thenCompose链中传递请求上下文，以修复slf4j中的MDC（类似于ThreadLocal，但在每次lambda运行之前重新应用，如下面的代码所示）。
public class Future<T> extends CompletableFuture<T> {@Overridepublic <U> CompletableFuture<U> thenApply(Function<? super T, ? extends U> fn) {Map<String, Object> state = FutureLocal.fetchState();MyFunction f = new MyFunction(state, fn);return super.thenApply(f);}@Overridepublic <U> CompletableFuture<U> thenCompose(Function<? super T, ? extends CompletionStage<U>> fn) {Map<String, Object> state = FutureLocal.fetchState();MyFunction f = new MyFunction(state, fn);return super.thenCompose(f);}// ... 其他方法 ...private class MyFunction implements Function {private Map<String, Object> state;private Function fn;public MyFunction(Map<String, Object> state, Function fn) {this.state = state;this.fn = fn;}@Overridepublic Object apply(Object t) {try {FutureLocal.restoreState(state);return fn.apply(t);} finally {FutureLocal.restoreState(null);}}}}
这是我用来运行上述代码的一些代码，但在映射中记录“test”开始在第3次远程调用时失败，这意味着slf4j MDC将会失效。
public class TestCustomFutures {private Executor exec = Executors.newFixedThreadPool(3);@Testpublic void testFutureContext() throws InterruptedException, ExecutionException {Set<Integer> hashSet = new HashSet<Integer>();FutureLocal.put("test", 100);CompletableFuture<Integer> f = myRemoteCall(4).thenCompose(s -> myRemoteCall(3)).thenCompose(s -> myRemoteCall(2));f.get();}private Future<Integer> myRemoteCall(int i) {System.out.println("result=" + i + " map=" + FutureLocal.get("test") + " thread=" + Thread.currentThread().getName());Future<Integer> f = new Future<Integer>();exec.execute(new Runnable() {@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {f.completeExceptionally(e);}f.complete(i);}});return f;}}
输出结果如下：
result=4 map=100 thread=mainresult=3 map=100 thread=pool-1-thread-1result=2 map=null thread=pool-1-thread-2
请注意，我们不希望最后一个值为null。
英文:
I have the following code which was kind of close except when I call super.thenCompose and it returns a CompletableFuture instead of my Custom Future.java which is kind of critical. I am trying to copy twitter's scala futures that
-
Be able to add cancellation chaining like twitter scala's futures
-
can have a request context flow through the thenApply and thenCompose chains to fix MDC in slf4j (much like a ThreadLocal but it is re-applied just before each lambda is run as seen in the code below)
public class Future<T> extends CompletableFuture<T> {
@Overridepublic <U> CompletableFuture<U> thenApply(Function<? super T, ? extends U> fn) {Map<String, Object> state = FutureLocal.fetchState();MyFunction f = new MyFunction(state, fn);return super.thenApply(f);}@Overridepublic <U> CompletableFuture<U> thenCompose(Function<? super T, ? extends CompletionStage<U>> fn) {Map<String, Object> state = FutureLocal.fetchState();MyFunction f = new MyFunction(state, fn);return super.thenCompose(f);}@SuppressWarnings("hiding")private class MyFunction implements Function {private Map<String, Object> state;private Function fn;public MyFunction(Map<String, Object> state, @SuppressWarnings("rawtypes") Function fn) {this.state = state;this.fn = fn;}@Overridepublic Object apply(Object t) {try {FutureLocal.restoreState(state);return fn.apply(t);} finally {FutureLocal.restoreState(null);}}}@Overridepublic boolean complete(T value) {return super.complete(value);}@Overridepublic boolean completeExceptionally(Throwable ex) {return super.completeExceptionally(ex);}
}
Here is some code I use to run that code but logging the "test" in the map starts failing on the 3rd remote call meaning slf4j MDC will break down.
public class TestCustomFutures {private Executor exec = Executors.newFixedThreadPool(3);@Testpublic void testFutureContext() throws InterruptedException, ExecutionException {Set<Integer> hashSet = new HashSet<Integer>();FutureLocal.put("test", 100);CompletableFuture<Integer> f = myRemoteCall(4).thenCompose(s -> myRemoteCall(3)).thenCompose(s -> myRemoteCall(2));f.get();}private Future<Integer> myRemoteCall(int i) {System.out.println("result="+i+" map="+FutureLocal.get("test")+" thread="+Thread.currentThread().getName());Future<Integer> f = new Future<Integer>();exec.execute(new Runnable() {@Overridepublic void run() {try {Thread.sleep(1000);} catch (InterruptedException e) {f.completeExceptionally(e);}f.complete(i);}});return f;}}
The output then is this
result=4 map=100 thread=mainresult=3 map=100 thread=pool-1-thread-1result=2 map=null thread=pool-1-thread-2
notice that last value we do not want to be null
答案1
得分: 0
ahhh，我错过了一个简单的东西，因为我在jdk8中。然而在jdk11中，您可以覆盖它...
@Overridepublic <U> CompletableFuture<U> newIncompleteFuture() {return new Future<U>();}
在jdk8中，由于某种原因，这段代码无法编译，并且不会调用这个方法 :(. 糟糕，我还不想升级到11，因为还有一些用法仍然在jdk8上 :(.
英文:
ahhh, I was missing one simple thing BECAUSE I was in jdk8. In jdk11 however, you can override this...
@Overridepublic <U> CompletableFuture<U> newIncompleteFuture() {return new Future<U>();}
In jdk8, for some reason, this would not compile and it would not invoke this :(. Crap, I didn't want to upgrade to 11 yet as some usages are stilll on jdk8 :(.
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