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[英]When using recursion in C#, is the code processed linearly or in pseudo parallel?
[英]Parallel recursion in c#
class CustomData
{
public int TNum;
public int TResult;
}
public static int F_recursion(int n, int w)
{
if (n == 0 || w == 0)
return 0;
else if (s[n] > w)
return F_recursion(n - 1, w);
else
{
return Math.Max(F_recursion(n - 1, w), p[n] + F_recursion(n - 1, w - s[n]));
}
}
public static int F_recursion2(int n, int w)
{
int numba = 0;
int countCPU = 8;
Task[] tasks = new Task[countCPU];
for (var j = 0; j < countCPU; j++)
tasks[j] = Task.Factory.StartNew(
(object p) =>
{
var data = p as CustomData; if (data == null) return;
data.TResult = F_recursion(n - data.TNum, w);
},
new CustomData() { TNum = j });
Task.WaitAll(tasks);
numba = (tasks[0].AsyncState as CustomData).TResult
+ (tasks[1].AsyncState as CustomData).TResult
+ (tasks[2].AsyncState as CustomData).TResult
+ (tasks[3].AsyncState as CustomData).TResult;
return numba;
}
我如何使F_recursion2方法並行工作? 用我的代碼當前結果是
Time in milliseconds for recursion: 1,075
recursion( 150 ) = 7,237
Time in milliseconds for parallel recursion: 1,581
recursion( 150 ) = 28,916
如您所見,並行方法打印的數字是原來的4倍,並且需要花費更多的時間來計算,這是沒有意義的。 我如何解決遞歸並行運行的問題?
編輯將for循環更改為Parallel.for仍然與上述結果相同。
public static int F_recursion2(int n, int w)
{
int numba = 0;
int countCPU = 8;
Task[] tasks = new Task[countCPU];
Parallel.For(0, countCPU, j =>
{
tasks[j] = Task.Factory.StartNew(
(object p) =>
{
var data = p as CustomData; if (data == null) return;
data.TResult = F_recursion(n - data.TNum, w);
},
new CustomData() { TNum = j });
});
Task.WaitAll(tasks);
numba = (tasks[0].AsyncState as CustomData).TResult
+ (tasks[1].AsyncState as CustomData).TResult
+ (tasks[2].AsyncState as CustomData).TResult
+ (tasks[3].AsyncState as CustomData).TResult;
return numba;
}
我想到的解決方案是使用Parallel.For
。 要做到這一點,你應該只是實現for
使用Parallel.For
。 要查看示例,請訪問此處 。
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