ConcurrentHashMap日常使用的例子

UserMgr.kt

/**
 * 当有很多用户同时登入和登出时，
 * onUserSignIn() 和 onUserSignOut() 就会有很多线程同时调用
 */
class UserMgr private constructor() {
    private val userMap: ConcurrentHashMap<String, User> = ConcurrentHashMap<String, User>()

    companion object {
        private val instance by lazy(LazyThreadSafetyMode.SYNCHRONIZED) { UserMgr() }

        fun Get() = instance
    }

    // 当用户登入时调用
    fun onUserSignIn(sessionId: String, user: User) {
        userMap[sessionId] = user
    }

    // 当用户登出或超时时调用
    fun onUserSignOut(sessionId: String) {
        userMap.remove(sessionId)
    }

    fun getUser(sessionId: String): User? = userMap[sessionId]
}