我正在阅读 tips and tricks发布,我想我会尝试一些我以前从未做过的 C# 东西。因此,下面的代码没有任何实际用途,只是一个“测试函数”,看看会发生什么。
无论如何,我有两个静态私有(private)字段:
private static volatile string staticVolatileTestString = "";
[ThreadStatic]
private static int threadInt = 0;
如您所见,我正在测试 ThreadStaticAttribute 和 volatile 关键字。
无论如何,我有一个看起来像这样的测试方法:
private static string TestThreadStatic() {
// Firstly I'm creating 10 threads (DEFAULT_TEST_SIZE is 10) and starting them all with an anonymous method
List<Thread> startedThreads = new List<Thread>();
for (int i = 0; i < DEFAULT_TEST_SIZE; ++i) {
Thread t = new Thread(delegate(object o) {
// The anon method sets a newValue for threadInt and prints the new value to the volatile test string, then waits between 1 and 10 seconds, then prints the value for threadInt to the volatile test string again to confirm that no other thread has changed it
int newVal = randomNumberGenerator.Next(10, 100);
staticVolatileTestString += Environment.NewLine + "\tthread " + ((int) o) + " setting threadInt to " + newVal;
threadInt = newVal;
Thread.Sleep(randomNumberGenerator.Next(1000, 10000));
staticVolatileTestString += Environment.NewLine + "\tthread " + ((int) o) + " finished: " + threadInt;
});
t.Start(i);
startedThreads.Add(t);
}
foreach (Thread th in startedThreads) th.Join();
return staticVolatileTestString;
}
我希望看到从这个函数返回的是这样的输出:
thread 0 setting threadInt to 88
thread 1 setting threadInt to 97
thread 2 setting threadInt to 11
thread 3 setting threadInt to 84
thread 4 setting threadInt to 67
thread 5 setting threadInt to 46
thread 6 setting threadInt to 94
thread 7 setting threadInt to 60
thread 8 setting threadInt to 11
thread 9 setting threadInt to 81
thread 5 finished: 46
thread 2 finished: 11
thread 4 finished: 67
thread 3 finished: 84
thread 9 finished: 81
thread 6 finished: 94
thread 7 finished: 60
thread 1 finished: 97
thread 8 finished: 11
thread 0 finished: 88
但是,我得到的是:
thread 0 setting threadInt to 88
thread 4 setting threadInt to 67
thread 6 setting threadInt to 94
thread 7 setting threadInt to 60
thread 8 setting threadInt to 11
thread 9 setting threadInt to 81
thread 5 finished: 46
thread 2 finished: 11
thread 4 finished: 67
thread 3 finished: 84
thread 9 finished: 81
thread 6 finished: 94
thread 7 finished: 60
thread 1 finished: 97
thread 8 finished: 11
thread 0 finished: 88
第二个“一半”的输出符合预期(我想这意味着 ThreadStatic 字段的工作方式与我想象的一样),但似乎一些初始输出已从第一个“一半”中“跳过” .
此外,前“半”中的线程是乱序的,但我知道线程不会在您调用 Start() 后立即运行;但是内部操作系统控件将在它认为合适的时候启动线程。
编辑:不,他们不是,实际上,我只是认为他们是因为我的大脑错过了连续的数字
所以,我的问题是:导致我在输出的前“一半”中丢失几行的问题是什么?例如,行“thread 3 setting threadInt to 84”在哪里?
最佳答案
多个线程同时执行。概念上发生的是这样的:
staticVolatileTestString += Environment.NewLine + "\tthread " + ((int) o) + " setting threadInt to " + newVal;
- 线程 1 读取 staticVolatileTestString
- 线程 2 读取 staticVolatileTestString
- 线程 3 读取 staticVolatileTestString
- 线程 1 追加内容并写回 staticVolatileTestString
- 线程 2 追加内容并写回 staticVolatileTestString
- 线程 3 追加内容并写回 staticVolatileTestString
这会导致您的台词丢失。 Volatile 在这里没有帮助;连接字符串的整个过程不是原子的。您需要对这些操作使用锁:
private static object sync = new object();
lock (sync) {
staticVolatileTestString += Environment.NewLine + "\tthread " + ((int) o) + " setting threadInt to " + newVal;
}
关于C# ThreadStatic + volatile 成员未按预期工作,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10993574/