272 lines
9.8 KiB
Markdown
272 lines
9.8 KiB
Markdown
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#unity/日常积累
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## 定义
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命名空间:
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[System.Threading](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading?view=net-8.0)
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程序集:
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System.Threading.dll
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以原子操作的形式递减指定变量的值并存储结果。
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[](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#--)
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## 重载
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展开表
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[Decrement(Int32)](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-int32@))
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以原子操作的形式递减指定变量的值并存储结果。
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[Decrement(Int64)](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-int64@))
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以原子操作的形式递减指定变量的值并存储结果。
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[Decrement(UInt32)](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-uint32@))
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以原子操作的形式递减指定变量的值并存储结果。
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[Decrement(UInt64)](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-uint64@))
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以原子操作的形式递减指定变量的值并存储结果。
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[](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-int32@))
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## Decrement(Int32)
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以原子操作的形式递减指定变量的值并存储结果。
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``` cs
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public static int Decrement (ref int location);
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```
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#### 参数
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location
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[Int32](https://learn.microsoft.com/zh-cn/dotnet/api/system.int32?view=net-8.0)
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其值要递减的变量。
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#### 返回
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[Int32](https://learn.microsoft.com/zh-cn/dotnet/api/system.int32?view=net-8.0)
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递减操作完成后紧接变量的值。
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#### 例外
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[ArgumentNullException](https://learn.microsoft.com/zh-cn/dotnet/api/system.argumentnullexception?view=net-8.0)
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`location` 的地址是一个 `null` 指针。
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[NullReferenceException](https://learn.microsoft.com/zh-cn/dotnet/api/system.nullreferenceexception?view=net-8.0)
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`location` 的地址是一个 `null` 指针。
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### 示例
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以下示例确定需要多少个介于 0 到 1,000 的随机数才能生成具有中点值的 1,000 个随机数。 为了跟踪中点值的数量，变量 `midpointCount`设置为等于 1,000，并在随机数生成器每次返回中点值时递减。 由于三个线程生成随机数， [Decrement(Int32)](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-int32@)) 因此调用 方法以确保多个线程不会同时更新 `midpointCount` 。 请注意，锁还用于保护随机数生成器，并使用 对象来确保`Main`方法不会在三个[CountdownEvent](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.countdownevent?view=net-8.0)线程之前完成执行。
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``` cs
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using System;
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using System.Threading;
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public class Example
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{
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const int LOWERBOUND = 0;
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const int UPPERBOUND = 1001;
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static Object lockObj = new Object();
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static Random rnd = new Random();
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static CountdownEvent cte;
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static int totalCount = 0;
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static int totalMidpoint = 0;
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static int midpointCount = 10000;
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public static void Main()
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{
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cte = new CountdownEvent(1);
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// Start three threads.
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for (int ctr = 0; ctr <= 2; ctr++) {
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cte.AddCount();
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Thread th = new Thread(GenerateNumbers);
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th.Name = "Thread" + ctr.ToString();
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th.Start();
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}
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cte.Signal();
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cte.Wait();
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Console.WriteLine();
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Console.WriteLine("Total midpoint values: {0,10:N0} ({1:P3})",
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totalMidpoint, totalMidpoint/((double)totalCount));
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Console.WriteLine("Total number of values: {0,10:N0}",
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totalCount);
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}
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private static void GenerateNumbers()
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{
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int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
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int value = 0;
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int total = 0;
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int midpt = 0;
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do {
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lock (lockObj) {
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value = rnd.Next(LOWERBOUND, UPPERBOUND);
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}
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if (value == midpoint) {
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Interlocked.Decrement(ref midpointCount);
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midpt++;
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}
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total++;
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} while (Volatile.Read(ref midpointCount) > 0);
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Interlocked.Add(ref totalCount, total);
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Interlocked.Add(ref totalMidpoint, midpt);
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string s = String.Format("Thread {0}:\n", Thread.CurrentThread.Name) +
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String.Format(" Random Numbers: {0:N0}\n", total) +
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String.Format(" Midpoint values: {0:N0} ({1:P3})", midpt,
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((double) midpt)/total);
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Console.WriteLine(s);
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cte.Signal();
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}
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}
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// The example displays output like the following:
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// Thread Thread2:
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// Random Numbers: 3,204,021
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// Midpoint values: 3,156 (0.099 %)
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// Thread Thread0:
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// Random Numbers: 4,073,592
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// Midpoint values: 4,015 (0.099 %)
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// Thread Thread1:
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// Random Numbers: 2,828,192
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// Midpoint values: 2,829 (0.100 %)
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//
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// Total midpoint values: 10,000 (0.099 %)
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// Total number of values: 10,105,805
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```
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下面的示例与上一个示例类似，只不过它使用 [Task](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.task?view=net-8.0) 类而不是线程过程来生成 50,000 个随机中点整数。 在此示例中，lambda 表达式替换了 `GenerateNumbers` 线程过程，对 方法的调用 [Task.WaitAll](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.tasks.task.waitall?view=net-8.0) 消除了对 [CountdownEvent](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.countdownevent?view=net-8.0) 对象的需要。
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``` cs
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using System;
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using System.Collections.Generic;
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using System.Threading;
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using System.Threading.Tasks;
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public class Example
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{
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const int LOWERBOUND = 0;
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const int UPPERBOUND = 1001;
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static Object lockObj = new Object();
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static Random rnd = new Random();
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static int totalCount = 0;
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static int totalMidpoint = 0;
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static int midpointCount = 50000;
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public static async Task Main()
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{
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List<Task> tasks = new List<Task>();
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// Start three tasks.
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for (int ctr = 0; ctr <= 2; ctr++)
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tasks.Add(Task.Run( () => { int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
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int value = 0;
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int total = 0;
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int midpt = 0;
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do {
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lock (lockObj) {
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value = rnd.Next(LOWERBOUND, UPPERBOUND);
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}
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if (value == midpoint) {
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Interlocked.Decrement(ref midpointCount);
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midpt++;
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}
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total++;
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} while (Volatile.Read(ref midpointCount) > 0);
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Interlocked.Add(ref totalCount, total);
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Interlocked.Add(ref totalMidpoint, midpt);
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string s = String.Format("Task {0}:\n", Task.CurrentId) +
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String.Format(" Random Numbers: {0:N0}\n", total) +
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String.Format(" Midpoint values: {0:N0} ({1:P3})", midpt,
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((double) midpt)/total);
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Console.WriteLine(s);
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} ));
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await Task.WhenAll(tasks.ToArray());
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Console.WriteLine();
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Console.WriteLine("Total midpoint values: {0,10:N0} ({1:P3})",
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totalMidpoint, totalMidpoint/((double)totalCount));
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Console.WriteLine("Total number of values: {0,10:N0}",
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totalCount);
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}
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}
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// The example displays output like the following:
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// Task 1:
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// Random Numbers: 24,530,624
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// Midpoint values: 24,675 (0.101 %)
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// Task 2:
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// Random Numbers: 7,079,718
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// Midpoint values: 7,093 (0.100 %)
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// Task 3:
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// Random Numbers: 18,284,617
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// Midpoint values: 18,232 (0.100 %)
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//
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// Total midpoint values: 50,000 (0.100 %)
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// Total number of values: 49,894,959
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```
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### 注解
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此方法通过包装处理溢出条件：如果 `location` = [Int32.MinValue](https://learn.microsoft.com/zh-cn/dotnet/api/system.int32.minvalue?view=net-8.0#system-int32-minvalue)， `location` 则 - 1 = 。 [Int32.MaxValue](https://learn.microsoft.com/zh-cn/dotnet/api/system.int32.maxvalue?view=net-8.0#system-int32-maxvalue) 不会引发异常。
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### 另请参阅
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- [托管线程](https://learn.microsoft.com/zh-cn/dotnet/standard/threading/)
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- [同步基元概述](https://learn.microsoft.com/zh-cn/dotnet/standard/threading/overview-of-synchronization-primitives)
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### 适用于
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.NET 8 和其他版本
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产品
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版本
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.NET
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Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8
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.NET Framework
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1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
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.NET Standard
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1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1
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UWP
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10.0
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Xamarin.iOS
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10.8
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Xamarin.Mac
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3.0
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[](https://learn.microsoft.com/zh-cn/dotnet/api/system.threading.interlocked.decrement?view=net-8.0#system-threading-interlocked-decrement(system-int64@))
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