Concurrent Debugging

Concurrent debugging, tools, containers!

references:

Tomcat7 optimize performance, improve concurrency -NIO mode

Singleton multithreading issues thoroughly get to know the interview asked of spring

A detailed understanding of singleton and multiple threads + A + interview questions inside tips

volatile keyword

• Volatile keyword effect (visibility of variables, reordering prohibited), can not be guaranteed atomicity

• scenes to be used
  • Usually modified state (boolean and int)
  • Simple assignment

Synchronization mechanism

• Monitor lock (the synchronized)

  Pessimistic locking

• Display lock (ReentrantLock, ReadWriteLock)

  Also provided in response to such an interrupt may be locked, the lock request may be a polling timing lock avoid deadlock Multithread

• Atomic variables (AtomicInteger, AtomicLong, AtomicBoolean)

  Optimistic locking, CAS (compare mention change)

• volatile

• Thread closed (analog single-threaded, multi-threaded environment aversion)

  Do not share data

  • Stack closed
  • ThreadLocal

Starting gun

CountDownLatch (thread counter)

static CountDownLatch cdl = new CountDownLatch(20);
...
    cdl.countDown();  // 此处要调用20次
...
cdl.await(); // 阻塞，countDown计数20次后才统一走下一步程序
// 类似发令枪，统一起跑

The default IO model and Tomcat8 the difference Tomcat7

BIO tomcat7 default, a thread corresponding to a request, blocked

tomcat8 the NIO default, a thread can handle multiple requests, nonblocking

• Start NIO mode

  Modify tomcat7 to NIO

  <Connector port="8080"protocol="org.apache.coyote.http11.Http11NioProtocol"
  
          connectionTimeout="20000" redirectPort="8443"/>

• Thread Pool

  The tomcat is not enabled by default thread pool, in tomcat each user request is a thread, so you can use the thread pool to improve performance. In fact, there is a reception here thread scheduling and dispatching thread into the thread pool, to a certain time and then to the thread pool task into a worker thread

  Release profile of the notes below, and specifies the actuators Connector

  <Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
          maxThreads="150" minSpareThreads="4"/>
  
  <!-- executor="tomcatThreadPool"为上面的执行器 -->
  <Connector executor="tomcatThreadPool" port="8080" protocol="HTTP/1.1"
                 connectionTimeout="20000"
                 redirectPort="8443" />

spring supports multithreading singleton

Why are local variables not affected by the impact of multi-threaded?

1. For those singleton class will run, such as Servlet Web multithreaded applications, each method of operation of a local variable is done in a thread of its own memory area, it is thread safe

2. Local variables are not affected by the impact multithreading

3. It will be multi-threaded member variables influence

4. For the operating member variables can be used to ensure the ThreadLocal thread safety

   ThreadLocal define a member variable in the bean object, the variable needs of member variables stored in a ThreadLocal