Scala怪異的性能問題

Question

我在scala中嘗試了一些東西，發現下面的代碼演示了奇怪的性能問題。這裏內聯一個函數調用使計算需要4倍的時間（4秒vs 16秒）。

package mypackage 

object MyObject extends Application { 
    class Complex(val real: Double, val imaginary: Double) { 
    def +(operand: Complex): Complex = { 
     new Complex(real + operand.real, imaginary + operand.imaginary) 
    } 
    def *(operand: Complex): Complex = { 
     new Complex(real * operand.real - imaginary * operand.imaginary, 
     real * operand.imaginary + imaginary * operand.real) 
    } 
    def mag2 = real * real + imaginary * imaginary 
    } 

    val iSize = 1250 
    val jSize = 1250 
    val xMin = -2.5 
    val xMax = +1.5 
    val yMin = -2.0 
    val yMax = +2.0 
    val dx = (xMax - xMin)/iSize 
    val dy = (yMax - yMin)/jSize 
    val steps = 50 

    def iterate(c: Complex) = { 
    var z = c 
    var n = 0 
    do { 
     z = z * z + c 
     n += 1 
    } while (n < steps && z.mag2 < 4.0) 
    } 

    // Mandelbrot set using iteration in a function. 
    var startTime = System.currentTimeMillis() 
    for (i <- 0 until iSize; j <- 0 until jSize) { 
    val c = new Complex(xMin + i * dx, yMin + j * dy) 
    iterate(c) 
    } 
    System.out.println("Elapsed time: " + (System.currentTimeMillis() - startTime)/1000.0 + " (s)") 

    // Mandelbrot set using iteration. 
    startTime = System.currentTimeMillis() 
    for (i <- 0 until iSize; j <- 0 until jSize) { 
    val c = new Complex(xMin + i * dx, yMin + j * dy) 
    var z = c 
    var n = 0 
    do { 
     z = z * z + c 
     n += 1 
    } while (n < steps && z.mag2 < 4.0) 
    } 
    System.out.println("Elapsed time: " + (System.currentTimeMillis() - startTime)/1000.0 + " (s)") 
} 

任何想法爲什麼會發生這種情況？ Interstingly在「迭代」函數之前添加「@inline」使其花費12 s vs 4 s。

Answer 1

請將應用程序替換爲應用程序，並獲得100倍加速。