Why do threads show better performance than coroutines?

Question

I wrote 3 simple programs to check coroutine performance over threads. Each program performs many simple simple calculations. All programs were launched separately from each other. Besides runtime, I measured CPU utilization through the Visual VMIDE plugin .

1. The first program performs all the calculations using the 1000-threadedpool. This code snippet shows worse results ( 64326 ms) compared to others due to frequent context changes:

   val executor = Executors.newFixedThreadPool(1000)
   time = generateSequence {
     measureTimeMillis {
       val comps = mutableListOf<Future<Int>>()
       for (i in 1..1_000_000) {
         comps += executor.submit<Int> { computation2(); 15 }
       }
       comps.map { it.get() }.sum()
     }
   }.take(100).sum()
   println("Completed in $time ms")
   executor.shutdownNow()
   

2. , 1000-threaded n-threaded ( n ). (43939 ms) , .

   val executor2 = Executors.newFixedThreadPool(4)
     time = generateSequence {
     measureTimeMillis {
       val comps = mutableListOf<Future<Int>>()
       for (i in 1..1_000_000) {
         comps += executor2.submit<Int> { computation2(); 15 }
       }
       comps.map { it.get() }.sum()
     }
   }.take(100).sum()
   println("Completed in $time ms")
   executor2.shutdownNow()
   

3. 41784 ms ( 41784 ms 81101 ms). , (, ). :

   time = generateSequence {
     runBlocking {
       measureTimeMillis {
         val comps = mutableListOf<Deferred<Int>>()
         for (i in 1..1_000_000) {
           comps += async { computation2(); 15 }
         }
         comps.map { it.await() }.sum()
       }
     }
   }.take(100).sum()
   println("Completed in $time ms")
   

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Answer 1

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}

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}

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}

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Answer 2

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Answer 3

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