C# 多线程 10-并行编程模式 01-实现惰性求值的共享状态
🏷️ 《C# 多线程》
示例代码
csharp
/// <summary>
/// 实现惰性求值的共享状态
/// </summary>
/// <param name="args"></param>
static void Main(string[] args)
{
var t = ProcessAsynchronously();
t.Wait();
Console.WriteLine("Press Enter to exit");
Console.ReadLine();
}
static async Task ProcessAsynchronously()
{
// 不安全的对象，构造方法会被调用了多次，
// 并且不同的线程中值是不同的
var unsafeState = new UnsafeState();
Task[] tasks = new Task[4];
for (int i = 0; i < 4; i++)
{
tasks[i] = Task.Run(() => Worker(unsafeState));
}
await Task.WhenAll(tasks);
Console.WriteLine("------------------------------");
// 使用双重锁定模式
var firstState = new DoubleCheckedLocking();
for (int i = 0; i < 4; i++)
{
tasks[i] = Task.Run(() => Worker(firstState));
}
await Task.WhenAll(tasks);
Console.WriteLine("------------------------------");
// 使用 LazyInitializer.EnsureInitialized 方法
var secondState = new BCLDoubleChecked();
for (int i = 0; i < 4; i++)
{
tasks[i] = Task.Run(() => Worker(secondState));
}
await Task.WhenAll(tasks);
Console.WriteLine("------------------------------");
// 使用 Lazy<T>类型
var lazy = new Lazy<ValueToAccess>(Compute);
var thirdState = new LazyWrapper(lazy);
for (int i = 0; i < 4; i++)
{
tasks[i] = Task.Run(() => Worker(thirdState));
}
await Task.WhenAll(tasks);
Console.WriteLine("------------------------------");
// 使用 LazyInitializer.EnsureInitialized 方法的一个不使用锁的重载
var fourthState = new BCLThreadSafeFactory();
for (int i = 0; i < 4; i++)
{
tasks[i] = Task.Run(() => Worker(fourthState));
}
await Task.WhenAll(tasks);
Console.WriteLine("------------------------------");
}
private static void Worker(IHasValue state)
{
Console.WriteLine($"Worker runs on thread id {Thread.CurrentThread.ManagedThreadId}");
Console.WriteLine($"State value: {state.Value.Text}");
}
class UnsafeState : IHasValue
{
private ValueToAccess _value;
// 不安全的对象，构造方法 Compute 会被调用多次
public ValueToAccess Value => _value ?? (_value = Compute());
}
class DoubleCheckedLocking : IHasValue
{
private readonly object _syncRoot = new object();
private volatile ValueToAccess _value;
public ValueToAccess Value
{
get
{
// 使用锁及双重验证，确保构造方法 Compute 仅执行一次
if (_value == null)
{
lock (_syncRoot)
{
if (_value == null)
{
_value = Compute();
}
}
}
return _value;
}
}
}
class BCLDoubleChecked : IHasValue
{
private object _syncRoot = new object();
private ValueToAccess _value;
private bool _initialized;
// 使用 LazyInitializer.EnsureInitialized 方法初始化
// 该方法内部实现了双重锁定模式
public ValueToAccess Value => LazyInitializer.EnsureInitialized(ref _value, ref _initialized, ref _syncRoot, Compute);
}
class BCLThreadSafeFactory : IHasValue
{
private ValueToAccess _value;
// 使用 LazyInitializer.EnsureInitialized 方法初始化
// 这个构造函数的重载没有使用锁，会导致初始化方法 Compute 被执行多次，但是结果的对象仍然是线程安全的
public ValueToAccess Value => LazyInitializer.EnsureInitialized(ref _value, Compute);
}
class LazyWrapper : IHasValue
{
// 使用 Lazy<T>类型
// 效果同使用 LazyInitializer 一样
// 区别是 LazyInitializer 是静态类，不需要初始化
private readonly Lazy<ValueToAccess> _value;
public LazyWrapper(Lazy<ValueToAccess> value)
{
_value = value;
}
public ValueToAccess Value => _value.Value;
}
static ValueToAccess Compute()
{
Console.WriteLine($"The value is being constructed on a thread id {Thread.CurrentThread.ManagedThreadId}");
Thread.Sleep(TimeSpan.FromSeconds(1));
return new ValueToAccess($"Constructed on thread id {Thread.CurrentThread.ManagedThreadId}");
}
interface IHasValue
{
ValueToAccess Value { get; }
}
class ValueToAccess
{
private readonly string _text;
public ValueToAccess(string text)
{
_text = text;
}
public string Text => _text;
}运行结果
txt
Worker runs on thread id 3
Worker runs on thread id 6
Worker runs on thread id 4
Worker runs on thread id 5
The value is being constructed on a thread id 3
The value is being constructed on a thread id 4
The value is being constructed on a thread id 5
The value is being constructed on a thread id 6
State value: Constructed on thread id 3
State value: Constructed on thread id 6
State value: Constructed on thread id 5
State value: Constructed on thread id 4
------------------------------
Worker runs on thread id 4
Worker runs on thread id 6
Worker runs on thread id 3
The value is being constructed on a thread id 4
Worker runs on thread id 5
State value: Constructed on thread id 4
State value: Constructed on thread id 4
State value: Constructed on thread id 4
State value: Constructed on thread id 4
------------------------------
Worker runs on thread id 5
Worker runs on thread id 4
Worker runs on thread id 6
Worker runs on thread id 7
The value is being constructed on a thread id 5
State value: Constructed on thread id 5
State value: Constructed on thread id 5
State value: Constructed on thread id 5
State value: Constructed on thread id 5
------------------------------
Worker runs on thread id 6
Worker runs on thread id 7
Worker runs on thread id 4
Worker runs on thread id 3
The value is being constructed on a thread id 6
State value: Constructed on thread id 6
State value: Constructed on thread id 6
State value: Constructed on thread id 6
State value: Constructed on thread id 6
------------------------------
Worker runs on thread id 7
Worker runs on thread id 6
Worker runs on thread id 3
The value is being constructed on a thread id 7
The value is being constructed on a thread id 3
Worker runs on thread id 4
The value is being constructed on a thread id 6
The value is being constructed on a thread id 4
State value: Constructed on thread id 7
State value: Constructed on thread id 7
State value: Constructed on thread id 7
State value: Constructed on thread id 7
------------------------------
Press Enter to exit