Java 8 parallel streams use the same threads for sequences
•
Java
Say we have such things:
LongStream.range(0,10).parallel()
.filter(l -> {
System.out.format("filter: %s [%s]\n",l,Thread.currentThread().getName());
return l % 2 == 0;
})
.map(l -> {
System.out.format("map: %s [%s]\n",Thread.currentThread().getName());
return l;
});
If you run this program, the output will be as follows:
filter: 6 [main] map: 6 [main] filter: 5 [main] filter: 4 [ForkJoinPool.commonPool-worker-2] map: 4 [ForkJoinPool.commonPool-worker-2] filter: 1 [ForkJoinPool.commonPool-worker-3] filter: 2 [ForkJoinPool.commonPool-worker-1] filter: 0 [ForkJoinPool.commonPool-worker-3] filter: 3 [ForkJoinPool.commonPool-worker-2] filter: 8 [main] filter: 7 [ForkJoinPool.commonPool-worker-2] filter: 9 [ForkJoinPool.commonPool-worker-2] map: 0 [ForkJoinPool.commonPool-worker-3] map: 2 [ForkJoinPool.commonPool-worker-1] map: 8 [main]`
As we can see, each task sequence of each long is executed by the same thread Is this something we can rely on, or is it a coincidence? Can threads share tasks during execution?
Solution
Side effects from the stream package summary section:
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