Is it thread-safe to set value to class member property in CompletableFuture callback?

I am new to CompletableFuture in Java 8 and I wonder whether the following code snippet is thread-safe when I set the result to class member properties in a callback, and try to read them after the allOf().get() call, and why?

CompletableFuture

allOf().get()

public void newInit() throws ExecutionException, InterruptedException {
CompletableFuture cf1 = CompletableFuture.supplyAsync(() -> {
return 1L;
}).thenAccept(result -> {
this.result1 = result;
});
CompletableFuture cf2 = CompletableFuture.supplyAsync(() -> {
return 2L;
}).thenAccept(result -> {
this.result2 = result;
});
CompletableFuture.allOf(cf1, cf2).get();
}


@DidierL I will read the values after CompletableFuture.allOf method, is it thread-safe?
– Chuck
Jun 28 at 6:25

1 Answer
1

Your question is covered by the Memory Consistency Properties defined on the java.util.concurrent package:

java.util.concurrent

Chapter 17 of the Java Language Specification defines the
happens-before relation on memory operations such as reads and writes of shared variables. The results of a write by one thread are
guaranteed to be visible to a read by another thread only if the write
operation happens-before the read operation. […]

The methods of all classes in java.util.concurrent and its
subpackages extend these guarantees to higher-level synchronization.
In particular:

java.util.concurrent

Future

Future.get()

So to summarize, your get() call guarantees that your writes will be visible to the thread after it performs it.

get()

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