引用的数据在复制后会重置为其默认值
本文关键字:默认值 数据 复制 引用 | 更新日期: 2023-09-27 18:20:24
我遇到一个问题,数据似乎被重置为默认值。类如下(objectID是一个简单的枚举):
public class Output_args: EventArgs {
public objectIDs outputtype;
public int internalID;
public int verdict;
public int outputID;
public long entrytime;
public Output_args Copy() {
Output_args args = new Output_args();
args.entrytime = this.entrytime;
args.internalID = this.internalID;
args.outputID = this.outputID;
args.outputtype = this.outputtype;
args.verdict = this.verdict;
return args;
}
}
下面的代码创建对象。它在一个特定的线程中运行,比如Thread1。
class Class1 {
EventWaitHandle ewh = new EventWaitHandle(false, EventResetMode.AutoReset);
public event EventHandler<Output_args> newOutput;
public void readInput(){
List<Output_args> newoutputlist = new List<Output_args>();
/*
* code to determine the outputs
*/
Output_args args = new Output_args();
args.outputtype = objectIDs.stepID;
args.internalID = step[s].ID;
args.verdict = verdict;
args.entrytime = System.DateTime.Now.Ticks;
newoutputlist.Add(args.Copy());
if (newOutput != null && newoutputlist.Count > 0) {
// several outputs are being sent sequentially but for simplicity i've removed the for-loop and decision tree
try {
newOutput(null, newoutputlist[0].Copy());
} catch (Exception) { }
}
}
}
此事件的1个订阅者具有以下代码。处理器方法在camerafeed的线程上运行。newOutput事件处理程序正在Thread1上运行。
class Class2: Form {
private Output_args lastoutput = new Output_args();
public void newOutput(object sender, Output_args args) {
lock (lastoutput) {
lastoutput = args.Copy();
}
}
public void processor(){
lock (lastoutput) {
if (lastoutput.entrytime + 10000000 > System.DateTime.Now.Ticks) {
// do something
}
}
}
}
当调用Class2的事件处理程序"newOutput"时,调试器会显示副本按预期工作,并为"entrytime"提供预期的刻度数
但是,当处理器方法想要读取"entrytime"时,其值为0。所有其他字段也指定了默认值
我试着用long类型的简单字段替换对象"lastoutput",并删除了锁,但结果是一样的:它在"newOutput"中得到了正确的赋值,但在processor方法中有其默认值(0)。
你知道为什么会这样吗?
您不应该锁定对象lastoutput
,而应该锁定另一个对象,因为您重新分配了字段。
处理器启动并锁定用默认值初始化的默认字段实例new Output_args()
class Class2: Form {
private object mylock = new object();
private Output_args lastoutput;
public void newOutput(object sender, Output_args args) {
lock (mylock) {
lastoutput = args.Copy();
}
}
public void processor(){
lock (mylock) {
if (lastoutput == null) {
//nothing to consume yet
}
else if (lastoutput.entrytime + 10000000 > System.DateTime.Now.Ticks) {
// do something
}
}
}
}
但如果消费者比生产者慢,则丢弃lastuput。如果需要,可以使用队列(或其他集合)作为缓冲区。
class Class2 {
private Queue<Output_args> outputs = new Queue<Output_args>();
public void newOutput(object sender, Output_args args) {
lock (outputs) {
outputs.Enqueue(args.Copy());
}
}
public void processor(){
lock (outputs) {
if (outputs.Count > 0) {
var lastoutput = outputs.Dequeue();
if (lastoutput.entrytime + 10000000 > System.DateTime.Now.Ticks) {
// do something
}
}
}
}
}
演示:https://dotnetfiddle.net/daHVD1