synchronization

问题 what is meant by vector in Java is thread safe and synchronized, how is it made thread safe. I'm looking at internal details of implementation 回答1: It is made "thread-safe" by merit of all its methods being synchronized (via the synchronized keyword), see the OpenJDK source code. What the synchronized keyword does is that it prevents more than one thread from executing any of the synchronized methods at the same time. It is using a lock internally, that a thread has to obtain when entering of

问题 I use Eclipse. When I have an application like this: write 20 times 'Hello World\n' to stdout write 'ERROR\n' to stderr write 5 times 'Hello World\n' to stdout The output looks many times like this: Hello World Hello World Hello World Hello World Hello World Hello World ... Hello World Hello World Hello World ERROR Is there a way to synchronize these two output streams? Of course without waiting a few milliseconds after the block of 20 times Hello World and waiting a few milliseconds after

问题 How does JVM make sure threads acquire a lock after entering synchronized method of an object? 回答1: Broad question: How does the JVM make sure...? The "VM" in "JVM" stands for "virtual machine." Your code doesn't do anything by itself. When we say, "your code runs", what we really mean is, the JVM executes your instructions. And it does so in accordance with the rules that are laid out in the JVM specification. One of the rules says that a JVM must never execute a synchronized block for two

问题 I have a stored procedure in mysql thats to perform a task that needs to be synchronized such that if two application calls the stored procedure, only one can access a section of code to perform the task, keeping the other one to get blocked until the first one finishes the task. DELIMITER $$ CREATE PROCEDURE SP_GEN_ID(IN NAME VARCHAR(20)) BEGIN DECLARE maxLen int default 0; START TRANSACTION; #the section of code that needs to be synchronized COMMIT END; $$ DELIMITER ; So, if two

问题 I have a Java Thread which exposes a property which other threads want to access: class MyThread extends Thread { private Foo foo; ... Foo getFoo() { return foo; } ... public void run() { ... foo = makeTheFoo(); ... } } The problem is that it takes some short time from the time this runs until foo is available. Callers may call getFoo() before this and get a null . I'd rather they simply block, wait, and get the value once initialization has occurred. ( foo is never changed afterwards.) It

问题 I'm trying to create a basic following algorithm using Swift and Firebase. My current implementation is the following: static func follow(user: FIRUser, userToFollow: FIRUser) { database.child("users").child(user.uid).observeSingleEventOfType(.Value, withBlock: { (snapshot) in var dbFollowing: NSMutableArray! = snapshot.value!["Following"] as! NSMutableArray! dbFollowing?.addObject(userToFollow.uid) self.database.child("users/"+(user.uid)+"/").updateChildValues(["Following":dbFollowing!]) /

问题 I am trying to implement very simple Windows events in Linux. Only for my scenario - 3 threads, 1 main and 2 secondary. Each of secondary threads raise 1 event by SetEvent and main thread wait it. Example: int main() { void* Events[2]; Events[0] = CreateEvent(); Events[1] = CreateEvent(); pthread_start(Thread, Events[0]); pthread_start(Thread, Events[1]); WaitForMultipleObjects(2, Events, 30000) // 30 seconds timeout return 0; } int* thread(void* Event) { // Do something SetEvent(Event); //

问题 Making every object lockable looks like a design mistake: You add extra cost for every object created, even though you'll actually use it only in a tiny fraction of the objects. Lock usage become implicit, having lockMap.get(key).lock() is more readable than synchronization on arbitrary objects, eg, synchronize (key) {...} . Synchronized methods can cause subtle error of users locking the object with the synchronized methods You can be sure that when passing an object to a 3rd parting API, it

问题 Lets say I have to orchestrate a synchronization algorithm in .Net 3.5 SP1 and any of the synchronization primitives listed in the title fit perfectly for the task. From a performance perspective, is any single one of those more performant than the others? I ask this because I have been coding for a while now, but without proper knowledge on the subject. 回答1: If you can, go with Monitor. It's similar to a CRITICAL_SECTION. AutoResetEvent/ManualResetEvent might have slightly more overhead,

问题 Suppose our application have only one thread. and we are using StringBuffer then what is the problem? I mean if StringBuffer can handle multiple threads through synchronization, what is the problem to work with single thread? Why use StringBuilder instead? 回答1: StringBuffers are thread-safe, meaning that they have synchronized methods to control access so that only one thread can access a StringBuffer object's synchronized code at a time. Thus, StringBuffer objects are generally safe to use