deadlock prevention

least one resource, but also made a new resource request, and the resource has been occupied by other processes, at this time the request process is blocked, but also to the other resources that they have obtained remain.(3) The inalienable condition: refers to the resources that the process has obtained, before being used, cannot be deprived, can only be released by oneself at the end of use.(4) Ring wait Condition: refers to a deadlock, there must

().getName()+" else locka"); } } } }}class MyLock{ static Object locka = new Object(); static Object lockb = new Object();}public class DieLockTest{ public static void main(String[] args) { Thread t1 = new Thread(new Test2(true)); Thread t2 = new Thread(new Test2(false)); t1.start(); t2.start(); }} The program that verifies that the lock of the synchronous function is this is also deadlocked: Class Test1 impleme

and maintain resourcesEach time the process requests a portion of the resources he needs, he continues to occupy the allocated resources while applying for new resources.(3) Non-looting of resourcesThe resources obtained by the process cannot be forcibly deprived by other processes until it is exhausted and can only be released voluntarily by the process(4) Cyclic waiting for resources.Also known as loop waiting. In the event of a deadlock, there mus

to a. Locking in order is an effective mechanism for deadlock prevention. However, this approach requires that you know beforehand all possible locks (translators: and do the proper sorting of these locks), but there are always times when it is unpredictable. Lock time limit Another way to avoid deadlocks is to add a time-out when trying to acquire a lock, which means that the thread discards the lock requ

4 conditions are met, a deadlock is guaranteed. Resource allocation diagram: To see if there is a deadlock in the clear. P->r solid line Application; r->p solid line distribution; P->r dashed demand.When there is only one instance per resource type, there is a ring equivalent to deadlock.When there are multiple instances of a resource type, a deadlock must have

of resources. The contention of locks will also lead to deadlocks. Deadlock examples (for better description, here we use locks as resources to describe the deadlock, here the lock is changed to resources completely OK) Self-deadlockAfter a process holds a lock, it applies for the lock again in the critical section. It will have to wait for the lock to be released, but because it is waiting for the lock

Prevention To avoid deadlocks, we can allocate resources in three ways to avoid deadlocks. 1. Static resource allocation: the process has applied for all the resources it needs before it starts execution, the process starts to run only when the system meets all the resource application requirements of the process and allocates the resources to the process. In this way, the two conditions of occupying and waiting for resources are destroyed, and the t

. 3. deadlock prevention: the deadlock prevention adopts a certain policy to restrict concurrent process requests to resources and destroy one of the four necessary conditions for deadlock, the system does not meet the deadlock co

One, deadlockDeadlock refers to a situation like this. When multiple threads compete for scarce resources, it is impossible for them to continue because they are waiting for the resources owned by each other's threads.The P2 process has R1 resources, but he is asking for R2 resources, while the P1 process has R2 resources, but he is requesting R1 resources.1.1 Coffman conditions--4 conditions for generating a deadlockIf the following 4 scenarios exist in a system, the chance of a

I. OverviewIn general, deadlock is an application design problem, by adjusting the business process, database object design, transaction size, and access to the database of SQL statements, the vast majority of deadlocks can be avoided, the following are a few common methods to avoid deadlocks.1. In the application, if different programs operate concurrently with multiple tables, you should try to agree to access the tables in the same order, which can

A deadlock occurs when multiple transactions hold and request locks on the same resource at the same time as a result of cyclic dependency. Deadlocks occur when a transaction attempts to lock a resource in a different order. Take the two transactions on the StockPrice table for example: Business 1 START TRANSACTION; UPDATE stockprice SET close = 45.50 WHERE stock_id = 4 and date = ' 2002-05-01 '; UPDATE stockprice SET close = 19.80 WHERE stoc

Find out the source of deadlock and blocking for SQL Server--Find out the source of SQL Server deadlock and blocking Copy Code code as follows: Use master Go declare @spid int, @bl int DECLARE S_cur CURSOR for Select 0, blocked From (SELECT * from sysprocesses where blocked>0) a Where NOT EXISTS (SELECT * from sysprocesses where blocked>0) b where A.blocked=spid) Union selec

This article is mainly through an experiment to describe, the process is more boring.Experiment PreparationCREATE TABLE Test_lock (ID int auto_increment PRIMARY key, stock int) Engine=innodb;Insert into Test_lock (id,stock) value (1,50);Here I make the stack information as simple as possible, the names of the 25 main functions and the entry parametersIn order to highlight the topic, I add this to the opening deadlock detection function list, altogeth

Deadlock Overview Typically, the simplest and most common deadlocks occur at different table levels,Session 1 The first step to modify a table, the second step to modify the B table,Session 2 The first step to modify the B table, the second step to modify a table,When the session 1 and Session 2 push sequence occurs when the deadlock occurs, this method of ending is relatively simple, in the same orde

run in different order and speed, and may also lead to deadlocks.Four Conditions for deadlock:(1)Mutex: A resource can only be used by one process at a time.(2)Request and persistence Conditions: When a process is blocked by requesting resources, it will not release the obtained resources.(3)Non-deprivation conditions: Resources obtained by the process cannot be forcibly deprived before they are used.(4)Cyclic wait Condition: A cyclical wait resource

Thread (new Test2 (false)); T1.start (); T2.start (); }}The program that verifies the synchronization function before the lock is this also becomes a deadlock:Class Test1 implements runnable{private static int num = 500; Object obj = new Object (); Boolean flag = true; public void Run () {if (flag) {while (true) {synchronized (obj)/ /Lock is obj {show ();//Lock Is this}}} else { while (true) {show (); }}} public synchronized void Show ()//Lock is

Deadlock (deadlock) Refers to two or more than two processes in the execution process, because of the contention for resources caused by a mutual waiting phenomenon, if there is no external force, they will not be able to proceed. At this point the system is in a deadlock state or the system generates a deadlock, and t

One, Live lockIf the transaction T1 block the data R, the transaction T2 also requests the Block R, so T2 waits. T3 also requested a blockade of R, when T1 released the blockade on R after the system first approved the T3 request, T2 still waits. Then T4 and asked to block R, when T3 released the blockade of R after the system also approved the T4 request, ..., T2 is likely to wait forever, this is the case of a live lock.A simple way to avoid a live lock is to use a first-come-first-serve strat

" conditions cannot be broken. Therefore, in deadlock prevention it is primarily to destroy the other three necessary conditions without involving the breach of the "mutually exclusive" condition. (2) Break the "request and hold" condition: the process is not allowed in the system to request additional resources if a resource has been obtained. The idea is to devise a way to prevent the process from request