Shulou(Shulou.com)06/03 Report--

Good programmers share the thread advanced part of big data's tutorial. Let's first talk about the life cycle of threads.

For a thread, after it is created, it does not immediately enter the running state, nor is it always running. In the thread's declaration cycle, a thread will switch between multiple states.

New: newborn state, thread is instantiated, but execution has not started (start)

Runnable: ready state, start has been executed, thread has been started, but did not grab the CPU time slice

Running: running status, grabbing CPU time slices

Blocked: blocking state, thread execution process, encountered some special circumstances, will enter the blocking state. Threads in blocking cannot be preempted by parameter time slices (cannot be scheduled by thread scheduler)

Dead: dead state, thread termination

​ normal death: end of code execution in the run method

​ abnormal death: force to stop this thread using the stop method

Critical resource problem

Because resources are shared between threads. If there are multiple threads that operate on a data at the same time, there will be a problem with that data.

If a thread is accessing a critical resource, it "locks" the resource before accessing it. At this time, if other threads also need to access the critical resource, you need to check whether the resource is locked. If it is not locked, the thread can access the resource; if it is locked, the thread enters a blocking state and waits for unlocking.

Synchronization code snippet / / synchronization code snippet / / parentheses: lock / / curly braces: synchronization code snippet, in general Synchronized () {} / about synchronization locks: can be divided into two types: object locks, class locks / / synchronization methods / / methods modified with the synchronized keyword are synchronization methods / / synchronize all code in a method / / equivalent to putting all code in a method into a synchronized code segment / / synchronization method locks: / / 1. If this method is a non-static method: the lock is this// 2. If this method is a static method: the lock is a class lock (current class .class) private synchronized void sellTicket () {} lock and unlock

It's just a RenntrantLock class.

Thread deadlock (understand)

In solving the critical resource problem, we introduce a concept of "lock". We can protect a resource with a lock. In fact, in a multithreaded environment, a situation may occur:

Suppose there are two threads An and B, where thread A holds the lock tag an and thread B holds the lock tag B. at this time, thread A waits for the release of the lock tag b, and thread B waits for the release of the lock tag a. This situation is called deadlock.

Producer-consumer design pattern

Wait (), notify (), notifyAll ()

Wait (): wait. Causes the current thread to release the lock mark and enter the waiting queue. You can put the current thread into a blocking state.

Notify (): wake up, wake up a thread in the waiting queue.

NotifyAll (): wake up, wake up all threads in the waiting queue.

The difference between wait and sleep:

Both methods can cause a thread to enter blocking.

Difference: the wait method releases the lock tag, while sleep does not release the lock tag. Thread Safety problems in lazy Singleton Design pattern Thread Pool

The ThreadPoolExecutor class is the core class of the thread pool. Several parameters in the constructor of this class:

Int corePoolSize: number of core threads. Core pool size.

Int maxmiunPoolSize: the maximum number of threads in the thread pool.

Long keepAliveTime: the amount of time that a temporary thread other than the core thread can survive. (from when this thread is idle)

TimeUnit unit: the unit of time above

​ NANOSECONDS: nanosecond

​ MICROSECONDS: microsecond

​ MILLISEONDS: milliseconds

​ SECONDS: seconds

​ MINUTES: points

​ HOURS: when

​ DAYS: God

BlockingQueue workQueue: waiting queue

​ ArrayBlockingQueue

​ LinkedBlockingQueue

​ SynchronousQueue

RejectedExecutionHandler handler: access denied policy

Preview directions:

Network programming

TCP

UDP

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