spring - @Synchronized似乎无法同步访问共享资源以进行对Spring Webserver的异步调用

Question

我有一个SpringBoot Web服务器；在其上的一条路由，用于控制单例实例的状态。通常由多个参与者调用此路由，因此必须进行同步。
路由调用的相应方法是set():

@Synchronized
public fun <T> set(t: T) {
    val incomingState = State.from(t)
    if(incomingState == innerState){
        return
    }
    change(incomingState)
}

@Synchronized
private fun change(newState: State){
    this.stateAccessLock.lock()
    SystemLog.logResourceLocking("HomeState", isLocked = true)
    SystemLog.logHomeEvent("Changing HomeState from '${innerState.name}' to '${newState.name}'")
    try {
        Home.INSTANCE.EXTENSION.broadcastStateChange(
            innerState?.name,
            newState.name
        )
    }
    finally {
        innerState = newState
        Home.save()

        stateAccessLock.unlock()
        SystemLog.logResourceLocking("HomeState", isLocked = false)
    }
}

在使用@Synchronized批注之前，我还尝试过在同一类中使用 ReentrantLock(如您所见，到目前为止，我忽略了将其删除)。初始化如下:

private var stateAccessLock = ReentrantLock()

@Autowired
fun HomeState(@Qualifier("stateAccessLock") stateAccessLock: ReentrantLock) {
    this.stateAccessLock = stateAccessLock
}

现在， change()中的第三行和最后一行记录了资源锁定并免费提供的资源。过滤这些事件的日志文件可以给我以下信息:

[2020-10-09T16:07:01.709]       LOCK: Resource locked
[2020-10-09T16:07:01.710]       LOCK: Resource locked
[2020-10-09T16:07:01.725]       LOCK: Resource locked
[2020-10-09T16:07:01.727]       LOCK: Resource locked
[2020-10-09T16:07:01.818]       LOCK: Resource unlocked
[2020-10-09T16:07:01.828]       LOCK: Resource unlocked
[2020-10-09T16:07:01.829]       LOCK: Resource unlocked
[2020-10-09T16:07:01.839]       LOCK: Resource unlocked
[2020-10-09T16:11:33.499]       LOCK: Resource locked
[2020-10-09T16:11:33.523]       LOCK: Resource locked
[2020-10-09T16:11:33.525]       LOCK: Resource locked
[2020-10-09T16:11:33.692]       LOCK: Resource unlocked
[2020-10-09T16:11:33.692]       LOCK: Resource unlocked
[2020-10-09T16:11:33.693]       LOCK: Resource unlocked
[2020-10-09T16:11:35.881]       LOCK: Resource locked
[2020-10-09T16:11:35.959]       LOCK: Resource unlocked

显然，我想要这样的东西:

[2020-10-09T16:07:01.709]       LOCK: Resource locked
[2020-10-09T16:07:01.710]       LOCK: Resource unlocked
[2020-10-09T16:07:01.725]       LOCK: Resource locked
[2020-10-09T16:07:01.727]       LOCK: Resource unlocked
[2020-10-09T16:07:01.818]       LOCK: Resource locked
[2020-10-09T16:07:01.828]       LOCK: Resource unlocked
[2020-10-09T16:07:01.829]       LOCK: Resource locked
[2020-10-09T16:07:01.839]       LOCK: Resource unlocked

我错过了什么？
提前致谢!

Answer 1

由于您不从这些方法中返回任何内容，因此我将改为进行线程限制并完全放弃锁定。这还将确保您不会陷入僵局:

private val executor = Executors.newSingleThreadExecutor()

fun <T> set(t: T) {
    executor.submit {
        val incomingState = State.from(t)
        if (incomingState == innerState) {
            return
        }
        change(incomingState)
    }
}

由于您具有单线程执行程序，因此可以确保以串行方式处理请求(并且没有锁定)。