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a synchronous lock, which is a built-in lock, or a lock is monitored, and a built-in lock is obtained by means of a synchronous method or block of code, that is, using the Synchronized keyword2). Display lockThe advanced locks provided by the JDK, such as lock, condition, etc., are mainly used for the functions of the built-in lock not easy to implement3. Some features of the lock1). Can be re-enteredJava Threads Compute locks on a per-thread basis, and in the same thread, you can enter the syn

Prior to Java5.0, only synchronized (built-in lock) and volatile. The display lock Reentrantlock is introduced after Java5.0. Reentrantlock OverviewThe Reentrantlock is a reentrant lock, which differs from the built-in lock, which needs to display the lock and unlock for each use, and provides more advanced features: Fair lock, timed lock, conditional lock, polling lock, interruptible lock. Can effectively avoid the deadlock of the active problem

33.1.1.1Telnet 33.1.1.1 80View commandsShow IP access-listsShow Class-mapShow Policy-mapShow Policy-map Interface S0/14. Queue technology (congestion management)Queue technology is applied to the direction of the interface, and an interface can use only one queue technology.There is a software queue and a hardware queue on the router's interface. The packet enters the soft queue first, and then the packet is dispatched into the hardware queue using the queue technology, and the hardware queue a

require immediate response and execution. such as video playback software or aircraft flight control system, it is obvious that such programs can not tolerate long delays in scheduling, light impact on the film screening effect, heavy machine destroyed human death.Linux uses different scheduling strategies based on the different classifications of the process. For real-time processes, a FIFO or Round Robin scheduling strategy is used. For normal processes, it is necessary to differentiate betwe

Reentrantlock Introduction Reentrantlock is a reentrant mutex, also known as an "exclusive lock." As the name suggests, Reentrantlock locks can only be held by a single thread lock at one point in time, and reentrant means that reentrantlock locks can be acquired multiple times by individual threads. Reentrantlock is divided into "fair lock" and "unjust lock". Their differences are reflected in the fairness of the mechanism for acquiring locks. "Lo

-queue-list 1R1#sh int f1/0Fastethernet1/0 is up, line protocol are upHardware is amdfe, address is cc00.2618.0010 (BIA cc00.2618.0010)Internet address is 192.168.12.1/24MTU bytes, BW 100000 Kbit, DLY usec,Reliability 255/255, Txload 1/255, Rxload 1/255Encapsulation ARPA, loopback not setKeepalive Set (SEC)Full-duplex, 100mb/s, 100basetx/fxARP Type:arpa, ARP Timeout 04:00:00Last input 00:00:00, output 00:00:01, output hang neverLast clearing of "show interface" counters neverInput queue:0/75/0/0

)//returns the string that identifies this semaphore, and the status of the semaphore. String toString ()//A license is obtained from the semaphore only if there is one available license for this semaphore at the time of invocation. BooleanTryacquire ()//These licenses are obtained from this semaphore only when there is a given number of licenses in this semaphore at the time of invocation. BooleanTryacquire (intpermits)//if all licenses are available for this semaphore within a given wait time,

indicating the status is 1, put the current thread into the waiting queue and block itself(After being awakenedLockMethod, and return to 1stStep to start again). Note: wakeup does not indicate that the thread can run immediately, but that the thread is in the ready state and can run. General process of thread release lock 1. The thread releasing the lock sets the value of the status variable from 1 to 0, and wakes upFirst NodeThe thread that releases the lock returns from the unlock method and

Now it is very popular to buy train tickets for the Spring Festival, and many sellers are eager to start marketing, such as using plug-ins to grab tickets. This article will discuss what is "fairness ". If the agent purchases tickets fairly, is it fair to look for leading backdoors and use scalpers to purchase tickets? Are there any essential differences in their nature? First remark: using advanced technologies to purchase tickets is a manifestation

Concurrentlinkedqueue, Synchronousqueue (fair mode) and Linkedblockingqueue. And LinkedTransferQueue is better, because it not only synthesizes the functions of these classes, but also provides a more efficient implementation.Joe Bowbeer offers a paper by William Scherer, Doug Lea, and Michael Scott, which shows the linkedtransferqueue algorithm in this paper, and the performance test results show that it is better than Java 5 of those classes (trans

0. PrefaceUnlike synchronized, lock is written entirely in Java and is not implemented by the JVM at the level of Java.In the Java.util.concurrent.locks package there are many implementation classes of lock, commonly used are reentrantlock, readwritelock (Implementation class Reentrantreadwritelock), Its realization all relies on the Java.util.concurrent.AbstractQueuedSynchronizer class, realizes the idea to be similar, therefore we take the Reentrantlock as the explanation entry point.1. Reentr

thread more flexible. using synchronized is equivalent to having only one single condition object in the entire lock object, all of which are registered on the body of one of its objects, when the thread starts Notifyall (), Need to notify all the waiting threads, there is no option, there will be a lot of efficiency problems. NBSP;46, condition implementation wait/notification: The Wait () method in the object class is equivalent to the await () method in the Condition class; the Notify (

This section is mainly about the implementation of read-write locks.As mentioned in the previous section, Readwritelock appears to have two locks: readlock/writelock. If it's really two locks, how do they affect each other?In fact, the realization of lock in Reentrantreadwritelock is done by Java.util.concurrent.locks.ReentrantReadWriteLock.Sync. This class looks familiar, in fact it is a subclass of Aqs, a similar structure that exists in Countdownlatch, Reentrantlock, and semaphore. It also ha

interrupted = false;for (;;) {Final Node p = node.predecessor ();if (p = = head tryacquire (ARG)) {Sethead (node);P.next = null; Help GCreturn interrupted;}if (Shouldparkafterfailedacquire (p, node) Parkandcheckinterrupt ())interrupted = true;}} catch (RuntimeException ex) {Cancelacquire (node);Throw ex;}} In Sethead , the predecessor node of the header is emptied and the thread of the head node is emptied for a better GC to prevent memory leaks. private void Sethead (node node) {Hea

One, Nginx load balancing algorithm1、轮询（默认） 每个请求按时间顺序逐一分配到不同的后端服务，如果后端某台服务器死机，自动剔除故障系统，使用户访问不受影响。2、weight（轮询权值） weight的值越大分配到的访问概率越高，主要用于后端每台服务器性能不均衡的情况下。或者仅仅为在主从的情况下设置不同的权值，达到合理有效的地利用主机资源。3、ip_hash 每个请求按访问IP的哈希结果分配，使来自同一个IP的访客固定访问一台后端服务器，并且可以有效解决动态网页存在的session共享问题。4、fair 比 weight、ip_hash更加智能的负载均衡算法，fair算法可以根据页面大小和加载时间长短智能地进行负载均衡，也就是根据后端服务器的响应时间 来分配请求，响应时间短的优先分配。Nginx本身不支持

current object. The following is an implementation of a blocking queue: public class blockqueue{ private List = new ArrayList (); Public synchronized Object POPs () throws interruptedexception{while (List.size () ==0) { this.wait (); } if (List.size () >0) {return list.remove (0); } else{return null; } Public synchronized object (object obj) { list.add (obj); This.notify (); } Synchronized with Wait (), notify () should be the basic skills that Java developer

With the popularity of MapReduce, the Open-source implementation of Hadoop has become increasingly popular. In a Hadoop system, it is important to have a component that is the scheduler that allocates the idle resources in the system to the job in a certain policy. In Hadoop, a scheduler is a pluggable module that allows users to design dispatchers according to their actual application requirements. There are three types of schedulers common in Hadoop, respectively: (Note: The Hadoop scheduler

thread that acquires the lock, increments the synchronization state and returns True, indicating that the synchronization state was successful.In the case of a fair lock, you also need to determine whether the current node in the synchronization queue has a precursor node, and if so, wait for the predecessor thread to acquire the lock and release it before continuing to acquire the lock.Fair lock and non-fair