差異處
這裏顯示兩個版本的差異處。
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java:java:java8:concurrent:blockingoperationwithcompletablefuture:build_chain_before_execution [2019/01/13 22:41] tony [How to resolve?] |
java:java:java8:concurrent:blockingoperationwithcompletablefuture:build_chain_before_execution [2023/06/25 09:48] |
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| - | {{tag>java concurrency}} | ||
| - | ====== CompletableFuture - It may be useful to build chain of actions before execution. ====== | ||
| - | ===== Problem ===== | ||
| - | 下方這隻程式在Java8中應是相當常見: | ||
| - | <code java> | ||
| - | CompletableFuture.supplyAsync(()->{ | ||
| - | dumpCurrentThreadName("supplyAsync"); | ||
| - | return new Response(); | ||
| - | }).whenComplete((response, ex)->{ | ||
| - | dumpCurrentThreadName("whenComplete"); | ||
| - | // process response | ||
| - | }); | ||
| - | </code> | ||
| - | 它的問題是如果supplyAsync中的工作，在執行whenComplete前就結束了；當執行whenComplete時，有可能會使用client thread去執行工作而影響到工作接收的速度。以下是我的執行結果: | ||
| - | <code> | ||
| - | ForkJoinPool.commonPool-worker-3: supplyAsync | ||
| - | main: whenComplete | ||
| - | </code> | ||
| - | 假如你的callback chain很長，遇到這個情況的機率就會越高。 | ||
| - | ===== How to resolve? ===== | ||
| - | 面對這個問題，在Java9中，允許你將實際的執行工作放到callback chain之後: | ||
| - | <code java> | ||
| - | CompletableFuture<Response> asyncJob = new CompletableFuture<>(); | ||
| - | |||
| - | asyncJob.whenComplete((response, ex)->{ | ||
| - | dumpCurrentThreadName("whenComplete"); | ||
| - | }); | ||
| - | |||
| - | asyncJob.completeAsync(()->{ | ||
| - | dumpCurrentThreadName("supplyAsync"); | ||
| - | return new Response(); | ||
| - | }); | ||
| - | </code> | ||
| - | 輸出結果如下: | ||
| - | <code> | ||
| - | ForkJoinPool.commonPool-worker-3: supplyAsync | ||
| - | ForkJoinPool.commonPool-worker-3: whenComplete | ||
| - | </code> | ||
| - | 這樣可以避免client thread跑去執行原本預期要async的工作，而增加了client thread的回應速度。\\ | ||
| - | \\ | ||
| - | 至於Java8就科科了。 | ||
| - | ===== Reference ===== | ||
| - | * [[https://qconsf.com/sf2017/system/files/presentation-slides/cf.pdf|Asynchronous API with | ||
| - | CompletableFuture - Performance Tips and Tricks]] | ||
| - | |||
| - | ====== ====== | ||
| - | ---- | ||
| - | \\ | ||
| - | ~~DISQUS~~ | ||
