synchronization

问题 Sync way For example, ruby: con = Mysql.new('localhost') rs1 = con.query('select * from test01') # A rs2 = con.query('select * from test02') # B rs = getResult(rs1, rs2) # C con.close so A will block the execution. B will be executed until A is done. So does C Async way for example, nodejs var mysql = require('mysql'); var connection = mysql.createConnection({host : 'localhost',}); connection.connect(); connection.query('SELECT * from test01', function(err, rows, fields) { console.log(rows);

问题 I am having an issue where Realm sometimes returns me different data every time I do the same query. Currently I am using an SyncAdapter for uploading. The idea is that we are trying to implement offline mode. So when the User creates an item it get's added to Realm db. I am generating the ID for that item manually by getting the maxId and adding 1000 to it. After that I am sending the itemID to the UploadSyncAdapter where I get the itemById and send it to the backend and the backend returns

问题 java.util.Collections currently provide the following utility methods for creating synchronized wrapper for various collection interfaces: synchronizedCollection(Collection<T> c) synchronizedList(List<T> list) synchronizedMap(Map<K,V> m) synchronizedSet(Set<T> s) synchronizedSortedMap(SortedMap<K,V> m) synchronizedSortedSet(SortedSet<T> s) Analogously, it also has 6 unmodifiedXXX overloads. The glaring omission here are the utility methods for NavigableMap<K,V>. It's true that it extends

问题 I am working with a client who is syncing between SQL Server and MySQL containing the exact same schema and data. We want to centralize that data into one database. Other then performance and maintainability issues, what else is bad about the original design? 回答1: You can create a linked server instance in SQL Server, with the MySQL instance. Despite being completely proprietary, one of the nice connectivity features offered in SQL Server is the ability to query other servers through a Linked

问题 What is the usage of synchronized statements? 回答1: It is a java built in form of mutual exclusion. This is used for multithreaded applications. Sun concurrency tutorial This has a section about synchronized, but you should read the whole thing if you are trying to use multithreaded applications. Wiki mutex 回答2: These are used for when you are building a program with many "threads". When main starts, it starts with one thread, which executes the steps in a sequence. You can start many more

问题 Imagine you have a typical producer-consumer pattern in Java. To be a bit more efficient you want to use notify() and not notifyAll() when a new element is added to the queue. If two producer threads invoke notify, is it guaranteed that two distinct waiting consumer threads will be awoken? Or can it be that two notify() s fired shortly after each other cause the same comsumer thread to be queued for wakeup twice? I can't find the section is the API describing how this exactly works. Does java

问题 I'm writing a program in Qt, which runs 10 worker threads which calculate the trajectory of an object in space. They also have to draw the path of the object. I have a "Body" class deriving QGraphicsEllipseItem and it has a QPainterPath in it. The "Simulation" class takes a list of obstacles in the world, and the body to simulate and runs until the body collides with something. Simulation runs in a separate thread ( done with moveToThread, not by subclassing QThread). When the body collides,

问题 I have a question regarding synchronization of code that is executed by several threads: As far as I know each thread has its own stack, hence, non-static variables exist in different locations in the memory for each thread (for X threads there are X stacks that include all non-static variables). So why there's a need to synchronize anything? I mean, if the code that the threads execute includes some class variable v1, then each thread has its own "instance" of v1 (different memory address),

问题 exampl: new Thread(new Runnable() { public void run() { while(condition) { *code that must not be interrupted* *some more code* } } }).start(); SomeOtherThread.start(); YetAntherThread.start(); How can you ensure that code that must not be interrupted won't be interrupted? 回答1: You can't - at least not with normal Java, running on a normal, non-real-time operating system. Even if other threads don't interrupt yours, other processes might well do so. Basically you won't be able to guarantee

问题 I was getting java.lang.IllegalMonitorStateException . I referred this question and it solved my problem. The first answer is To be able to call notify() you need to synchronize on the same object. synchronized (someObject) { someObject.wait(); } /* different thread / object */ synchronized (someObject) { someObject.notify(); } My question is why we need to synchronize on the same object ad how it works? As far as my understanding goes when we say synchronized (someObject) { someObject.wait()