如何在C#中获得最佳性能的线程安全计数器?
这很简单:
public static long GetNextValue()
{
long result;
lock (LOCK)
{
result = COUNTER++;
}
return result;
}
但是是否有更快的替代方案呢?
如何在C#中获得最佳性能的线程安全计数器?
这很简单:
public static long GetNextValue()
{
long result;
lock (LOCK)
{
result = COUNTER++;
}
return result;
}
但是是否有更快的替代方案呢?
Interlocked.Increment
的性能比lock()
更好。只需看一下IL和Assembly,就会发现Increment
转换成了“总线锁”语句,并且它的变量直接增加(x86)或者“添加”(x64)。lock()
语句的IL,您将看到调用Monitor
以开始或结束一个代码块。lock()
语句执行的操作比 .Net Interlocked.Increment
多得多。Interlocked.Increment
会更快。查看所有Interlocked方法以查看可用的各种原子操作,并找到适合您需要的操作。当您要执行多个相互关联的递增/递减,或串行访问比整数更复杂的资源时,请使用lock()
。我建议您使用 .NET 的内置原子增量在 System.Threading 库中。
以下代码将通过引用递增长整型变量,并完全保证线程安全:
Interlocked.Increment(ref myNum);
如前所述,请使用Interlocked.Increment
来自微软的代码示例:
以下示例确定需要多少个介于0到1,000之间的随机数才能生成1,000个具有中点值的随机数。为了跟踪中点值的数量,将一个变量midpointCount设置为0,并在随机数生成器返回中点值时递增,直到达到10,000。由于三个线程生成随机数,因此调用Increment(Int32)方法以确保多个线程不会同时更新midpointCount。请注意,还使用锁来保护随机数生成器,并使用CountdownEvent对象确保Main方法在三个线程之前完成执行。
using System;
using System.Threading;
public class Example
{
const int LOWERBOUND = 0;
const int UPPERBOUND = 1001;
static Object lockObj = new Object();
static Random rnd = new Random();
static CountdownEvent cte;
static int totalCount = 0;
static int totalMidpoint = 0;
static int midpointCount = 0;
public static void Main()
{
cte = new CountdownEvent(1);
// Start three threads.
for (int ctr = 0; ctr <= 2; ctr++) {
cte.AddCount();
Thread th = new Thread(GenerateNumbers);
th.Name = "Thread" + ctr.ToString();
th.Start();
}
cte.Signal();
cte.Wait();
Console.WriteLine();
Console.WriteLine("Total midpoint values: {0,10:N0} ({1:P3})",
totalMidpoint, totalMidpoint/((double)totalCount));
Console.WriteLine("Total number of values: {0,10:N0}",
totalCount);
}
private static void GenerateNumbers()
{
int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
int value = 0;
int total = 0;
int midpt = 0;
do {
lock (lockObj) {
value = rnd.Next(LOWERBOUND, UPPERBOUND);
}
if (value == midpoint) {
Interlocked.Increment(ref midpointCount);
midpt++;
}
total++;
} while (midpointCount < 10000);
Interlocked.Add(ref totalCount, total);
Interlocked.Add(ref totalMidpoint, midpt);
string s = String.Format("Thread {0}:\n", Thread.CurrentThread.Name) +
String.Format(" Random Numbers: {0:N0}\n", total) +
String.Format(" Midpoint values: {0:N0} ({1:P3})", midpt,
((double) midpt)/total);
Console.WriteLine(s);
cte.Signal();
}
}
// The example displays output like the following:
// Thread Thread2:
// Random Numbers: 2,776,674
// Midpoint values: 2,773 (0.100 %)
// Thread Thread1:
// Random Numbers: 4,876,100
// Midpoint values: 4,873 (0.100 %)
// Thread Thread0:
// Random Numbers: 2,312,310
// Midpoint values: 2,354 (0.102 %)
//
// Total midpoint values: 10,000 (0.100 %)
// Total number of values: 9,965,084
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
const int LOWERBOUND = 0;
const int UPPERBOUND = 1001;
static Object lockObj = new Object();
static Random rnd = new Random();
static int totalCount = 0;
static int totalMidpoint = 0;
static int midpointCount = 0;
public static void Main()
{
List<Task> tasks = new List<Task>();
// Start three tasks.
for (int ctr = 0; ctr <= 2; ctr++)
tasks.Add(Task.Run( () => { int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
int value = 0;
int total = 0;
int midpt = 0;
do {
lock (lockObj) {
value = rnd.Next(LOWERBOUND, UPPERBOUND);
}
if (value == midpoint) {
Interlocked.Increment(ref midpointCount);
midpt++;
}
total++;
} while (midpointCount < 50000);
Interlocked.Add(ref totalCount, total);
Interlocked.Add(ref totalMidpoint, midpt);
string s = String.Format("Task {0}:\n", Task.CurrentId) +
String.Format(" Random Numbers: {0:N0}\n", total) +
String.Format(" Midpoint values: {0:N0} ({1:P3})", midpt,
((double) midpt)/total);
Console.WriteLine(s); } ));
Task.WaitAll(tasks.ToArray());
Console.WriteLine();
Console.WriteLine("Total midpoint values: {0,10:N0} ({1:P3})",
totalMidpoint, totalMidpoint/((double)totalCount));
Console.WriteLine("Total number of values: {0,10:N0}",
totalCount);
}
}
// The example displays output like the following:
// Task 3:
// Random Numbers: 10,855,250
// Midpoint values: 10,823 (0.100 %)
// Task 1:
// Random Numbers: 15,243,703
// Midpoint values: 15,110 (0.099 %)
// Task 2:
// Random Numbers: 24,107,425
// Midpoint values: 24,067 (0.100 %)
//
// Total midpoint values: 50,000 (0.100 %)
// Total number of values: 50,206,378
https://learn.microsoft.com/en-us/dotnet/api/system.threading.interlocked.increment?view=netcore-3.0