C#复习⑧

C#复习⑧

2016年6月22日

13:50

Main Attribute & Threads 属性与线程

1.Conditional Attribute 条件属性

#define debug         // preprocessor directive
 
class C {
 
[Conditional("debug")]        // only possible for void methods
 
static void Assert (bool ok, string errorMsg) {
 
if (!ok) {
 
Console.WriteString(errorMsg);
 
System.Environment.Exit();
 
}
 
}
 
static void Main (string[] arg) {
 
Assert(arg.Length > , "no arguments specified");
 
Assert(arg[] == "...", "invalid argument");
 
...
 
}
 
}

断言仅被调用，如果定义了debug。

Assert is only called, if debug was defined.

还可用于控制跟踪输出。

Also useful for controlling trace output.

2.Serialization 序列化

3.AttributeUsage

定义自己的Attribute：

4.线程

声明一个线程：

//假设有方法void M(){}
 
Thread t = new Thread(M);
 
t.Start(); //线程执行

5.Type类型

public sealed class Thread {
 
public static Thread CurrentThread { get; }        // static properties and methods
 
public static void Sleep(int milliSeconds) {...}
 
...
 
public Thread(ThreadStart startMethod) {...}        // thread creation
 
public string Name { get; set; }        // properties
 
public ThreadPriority Priority { get; set; }
 
public ThreadState ThreadState { get; }
 
public bool IsAlive { get; }
 
public bool IsBackground { get; set; }
 
...
 
public void Start() {...}        // methods
 
public void Suspend() {...}
 
public void Resume() {...}
 
public void Join() {...}        // t.Join(): caller waits for t to die
 
public void Abort() {...}        // throws ThreadAbortException
 
public void Interrupt() {...}        // callable in WaitSleepState
 
...
 
}
 
public delegate void ThreadStart();        // parameterless void method
 
public enum ThreadPriority {Normal, AboveNormal, BelowNormal, Highest, Lowest}
 
public enum ThreadState {Unstarted, Running, Suspended, Stopped, Aborted, ...}

举例：

using System;
 
using System.Threading;
 
class Printer {
 
char ch;
 
int sleepTime;
 
public Printer(char c, int t) {ch = c; sleepTime = t;}
 
public void Print() {
 
for (int i = ; i < ; i++) {
 
Console.Write(ch);
 
Thread.Sleep(sleepTime);
 
　　　　}
 
　　}
 
}
 
class Test {
 
static void Main() {
 
Printer a = new Printer('.', );
 
Printer b = new Printer('*', );
 
new Thread(a.Print).Start();
 
new Thread(b.Print).Start();
 
　　}
 
}

6.与Java的不同之处

7.线程的状态以及相互转化

using System;
 
using System.Threading;
 
class Test {
 
static void P() {
 
for (int i = ; i < ; i++) {
 
Console.Write('-');
 
Thread.Sleep();
 
　　}
 
}
 
static void Main() {
 
Thread t = new Thread(P);
 
Console.Write("start");
 
t.Start();
 
t.Join(); // waits until t has finished
 
Console.WriteLine("end");
 
　　}
 
}
 
//Output
 
// start--------------------end

using System; using System.Threading;
 
class Test {
 
static void P() {
 
try {
 
try {
 
try {
 
while (true) ;
 
　　} catch (ThreadAbortException) { Console.WriteLine("-- inner aborted"); }
 
　　　　} catch (ThreadAbortException) { Console.WriteLine("-- outer aborted"); }
 
　　　　　　} finally { Console.WriteLine("-- finally"); }
 
}
 
static void Main(string[] arg) {
 
Thread t = new Thread(P);
 
t.Start(); Thread.Sleep();
 
t.Abort(); t.Join(); Console.WriteLine("done");
 
　　}
 
}
 
/*Output
 
-- inner aborted
 
-- outer aborted
 
-- finally
 
done*/

8.互斥Mutual Exclusion

一次只能有一个线程掌握着该锁。直到该锁被释放才能被其他线程调用。

举例：

class Account {        // this class is a monitor
 
long val = ;
 
public void Deposit(long x) {
 
lock (this) { val += x; }        // only 1 thread at a time may execute this statement
 
}
 
public void Withdraw(long x) {
 
lock (this) { val -= x; }
 
　　}
}

锁可以加在任何类型上：

object semaphore = new object();

...

lock (semaphore) { ... critical region ... }

9.Wait and Pulse

Monitor.Wait(lockedVar);       // 大致等于wait() in Java (in Java lockedVar is always this)
 
Monitor.Pulse(lockedVar);        //大致等于 notify() in Java
 
Monitor.PulseAll(lockedVar);       // 大致等于 notifyAll() in Java

举例：

PulseAll(v)唤醒所有等待的线程的V，但其中只有一个是允许继续。其他线程必须等待，直到前一个释放了锁。然后，下一个线程可能进入执行。

PulseAll(v) wakes up all threads that wait for v, but only one of them is allowed to continue. The others must wait until the previous one has released the lock. Then the next thread may enter the critical region.

举例：