我有一个对象的地图,这些对象的创建成本很高,所以我想创建对象并与我的应用程序中的其他进程并行填充地图.只有当主线程实际需要访问映射时,应用程序才会等待填充映射的异步任务完成.我怎样才能最优雅地完成这项工作?
目前的做法
目前,我能够在下面的示例代码中使用CompletableFuture.runAsync(Runnable, Executor)
类似于异步创建地图本身中的每个单独对象,但我不确定如何构建Future / CompletableFuture类型机制,以便在准备好时返回Map本身:
public static class AsynchronousMapPopulator {
private final Executor backgroundJobExecutor;
public AsynchronousMapPopulator(final Executor backgroundJobExecutor) {
this.backgroundJobExecutor = backgroundJobExecutor;
}
public ConcurrentMap<String, Integer> apply(final Map<String,Integer> input) {
final ConcurrentMap<String, Integer> result = new ConcurrentHashMap<>(input.size());
final Stream.Builder<CompletableFuture<Void>> incrementingJobs = Stream.builder();
for (final Entry<String, Integer> entry : input.entrySet()) {
final String className = entry.getKey();
final Integer oldValue = entry.getValue();
final CompletableFuture<Void> incrementingJob = CompletableFuture.runAsync(() -> {
result.put(className, oldValue + 1);
}, backgroundJobExecutor);
incrementingJobs.add(incrementingJob);
}
// TODO: This blocks until the training is done; Instead, return a
// future to the caller somehow
CompletableFuture.allOf(incrementingJobs.build().toArray(CompletableFuture[]::new)).join();
return result;
}
}
但是,使用上面的代码,当代码调用AsynchronousTest.create(Map< String,Integer)时,它已经阻塞,直到该方法返回完全填充的ConcurrentMap< String,Integer> ;;如何将其转换为Future< Map< String,Integer>>以便我以后可以使用它?:
Executor someExecutor = ForkJoinPool.commonPool();
Future<Map<String,Integer>> futureClassModels = new AsynchronousMapPopulator(someExecutor).apply(wordClassObservations);
...
// Do lots of other stuff
...
Map<String,Integer> completedModels = futureClassModels.get();
最佳答案 正如@Holger在他的评论中所述,你必须避免调用.join()并依赖于thenApply(),例如像这样:
public static class AsynchronousMapPopulator {
private final Executor backgroundJobExecutor;
public AsynchronousMapPopulator(final Executor backgroundJobExecutor) {
this.backgroundJobExecutor = backgroundJobExecutor;
}
public Future<Map<String, Integer>> apply(final Map<String,Integer> input) {
final ConcurrentMap<String, Integer> result = new ConcurrentHashMap<>(input.size());
final Stream.Builder<CompletableFuture<Void>> incrementingJobs = Stream.builder();
for (final Entry<String, Integer> entry : input.entrySet()) {
final String className = entry.getKey();
final Integer oldValue = entry.getValue();
final CompletableFuture<Void> incrementingJob = CompletableFuture.runAsync(() -> {
result.put(className, oldValue + 1);
}, backgroundJobExecutor);
incrementingJobs.add(incrementingJob);
}
// using thenApply instead of join here:
return CompletableFuture.allOf(
incrementingJobs.build().toArray(
CompletableFuture[]::new
)
).thenApply(x -> result);
}
}