如何在 C# 中编写条件锁？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/243152/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How can I write a conditional lock in C#?
提问by sebagomez
The thing is I've been using the lock statementto protect a critical part of my code, but now, I realize I could allow concurrent execution of that critical code is some conditions are met.
Is there a way to condition the lock?
问题是我一直在使用lock 语句来保护我的代码的关键部分，但是现在，我意识到如果满足某些条件，我可以允许该关键代码的并发执行。
有没有办法调节锁？
采纳答案by Amy B
Action doThatThing = someMethod;
if (condition)
{
lock(thatThing)
{
doThatThing();
}
}
else
{
doThatThing();
}
回答by noocyte
I'm guessing you've got some code that looks a little like this:
我猜你有一些看起来像这样的代码：
private Monkey GetScaryMonkey(int numberOfHeads){
Monkey ape = null;
lock(this) {
ape = new Monkey();
ape.AddHeads(numberOfHeads);
}
return ape;
}
To make this conditional couldn't you just do this:
为了使这个有条件，你不能这样做：
private Monkey GetScaryMonkey(int numberOfHeads){
if ( numberOfHeads > 1 ) {
lock(this) {
return CreateNewMonkey( numberOfHeads );
}
}
return CreateNewMonkey( numberOfHeads );
}
Should work, no?
应该工作，不是吗？
回答by Tomalak
I think that question cries "race condition!". What if the condition turns from true to false shortly after the check, but before a thread enters the critical section of code? Or while a thread is in the process of executing it?
我认为这个问题叫“竞争条件！”。如果条件在检查后不久、但在线程进入代码的临界区之前从真变为假怎么办？或者当一个线程正在执行它的过程中？
回答by Marc Gravell
Actually, to avoid a race condition, I'd be tempted to use a ReaderWriterLockSlimhere - treat concurrent access as a read lock, and exclusive access as a write lock. That way, if the conditions change you won't end up with some inappropriate code still executing blindly in the region (under the false assumption that it is safe); a bit verbose, but
(formatted for space):
实际上，为了避免竞争条件，我很想在ReaderWriterLockSlim此处使用- 将并发访问视为读锁，将排他访问视为写锁。这样，如果条件发生变化，您最终不会在该区域中盲目执行一些不适当的代码（假设它是安全的）；有点冗长，但是（格式化为空格）：
if (someCondition) {
lockObj.EnterReadLock();
try { Foo(); }
finally { lockObj.ExitReadLock(); }
} else {
lockObj.EnterWriteLock();
try { Foo(); }
finally { lockObj.ExitWriteLock(); }
}
回答by marijne
bool locked = false;
if (condition) {
Monitor.Enter(lockObject);
locked = true;
}
try {
// possibly critical section
}
finally {
if (locked) Monitor.Exit(lockObject);
}
EDIT: yes, there is a race condition unless you can assure that the condition is constant while threads are entering.
编辑：是的，除非您可以确保在线程进入时条件保持不变，否则存在竞争条件。
回答by user31934
I'm no threading expert, but it sounds like you might be looking for something like this (double-checked locking). The idea is to check the condition both before and after acquiring the lock.
我不是线程专家，但听起来您可能正在寻找这样的东西（双重检查锁定）。这个想法是在获取锁之前和之后检查条件。
private static object lockHolder = new object();
if (ActionIsValid()) {
lock(lockHolder) {
if (ActionIsValid()) {
DoSomething();
}
}
}
回答by Pure.Krome
Use Double-checked locking pattern, as suggested above. that's the trick IMO :)
如上所述，使用双重检查锁定模式。这就是海事组织的诀窍:)
make sure you have your lock object as a static, as listed in not.that.dave.foley.myopenid.com's example.
确保您的锁对象为static，如 not.that.dave.foley.myopenid.com 的示例中所列。
