synchronization | 易学教程

How to add programmatically a custom account in android?

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问题 I am trying to create an account for my app, where I will be able to have my contacts against my account like facebook, viber, whatsapp etc. I want my account to be visible in the account section of the settings also. Any ideas? I have googled a lot, but couldn\'t find a right answer where to start. Please help. What I have tried to create an account is as below. Which leads me to an error. Account account = new Account(\"Title\", \"com.package.nom\"); String password = \"password\";

Synchronous request in Node.js

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问题 If I need to call 3 http API in sequential order, what would be a better alternative to the following code: http.get({ host: \'www.example.com\', path: \'/api_1.php\' }, function(res) { res.on(\'data\', function(d) { http.get({ host: \'www.example.com\', path: \'/api_2.php\' }, function(res) { res.on(\'data\', function(d) { http.get({ host: \'www.example.com\', path: \'/api_3.php\' }, function(res) { res.on(\'data\', function(d) { }); }); } }); }); } }); }); } 回答1: Using deferreds like

How to share semaphores between processes using shared memory

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问题 I have to synchronize N client processes with one server. These processes are forked by a main function in which I declared 3 semaphores. I decided to use POSIX semaphores but I don\'t know how to share them between these processes. I thought that shared memory should work correctly, but I have some questions: How can I allocate the right space of memory in my segment? Can I use sizeof(sem_t) in size_t field of shmget in order to allocate exactly the space I need? Does anyone have some

Wait until flag=true

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问题 I have javascript function like this: function myFunction(number) { var x=number; ... ... more initializations //here need to wait until flag==true while(flag==false) {} ... ... do something } The problem is that the javascript is stuck in the while and stuck my program. so my question is how can I wait in the middle of the function until flag is true without \"busy-wait\"? 回答1: Because javascript in a browser is single threaded (except for webworkers which aren't involved here) and one

How do synchronized static methods work in Java?

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If I have a util class with static methods that will call Hibernate functions to accomplish basic data access. I am wondering if making the method synchronized is the right approach to ensure thread-safety. I want this to prevent access of info to the same DB instance. However, I'm now sure if the following code are preventing getObjectById being called for all Classes when it is called by a particular class. public class Utils { public static synchronized Object getObjectById (Class objclass, Long id) { // call hibernate class Session session = new Configuration().configure()

Is multi-thread output from System.out.println interleaved

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问题 If multiple threads call System.out.println(String) without synchronization, can the output get interleaved? Or is the write of each line atomic? The API makes no mention of synchronization, so this seems possible, or is interleaved output prevented by buffering and/or the VM memory model, etc.? EDIT: For example, if each thread contains: System.out.println(\"ABC\"); is the output guaranteed to be: ABC ABC or could it be: AABC BC 回答1: Since the API documentation makes no mention of thread

Printing Even and Odd using two Threads in Java

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问题 I tried the code below. I took this piece of code from some other post which is correct as per the author. But when I try running, it doesn\'t give me the exact result. This is mainly to print even and odd values in sequence. public class PrintEvenOddTester { public static void main(String ... args){ Printer print = new Printer(false); Thread t1 = new Thread(new TaskEvenOdd(print)); Thread t2 = new Thread(new TaskEvenOdd(print)); t1.start(); t2.start(); } } class TaskEvenOdd implements

How do determine if an object is locked (synchronized) so not to block in Java?

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问题 I have a process A that contains a table in memory with a set of records (recordA, recordB, etc...) Now, this process can launch many threads that affect the records, and sometimes we can have 2 threads trying to access the same record - this situation must be denied. Specifically if a record is LOCKED by one thread I want the other thread to abort (I do not want to BLOCK or WAIT). Currently I do something like this: synchronized(record) { performOperation(record); } But this is causing me

When should we use mutex and when should we use semaphore

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问题 When should we use mutex and when should we use semaphore ? 回答1: Here is how I remember when to use what - Semaphore: Use a semaphore when you (thread) want to sleep till some other thread tells you to wake up. Semaphore 'down' happens in one thread (producer) and semaphore 'up' (for same semaphore) happens in another thread (consumer) e.g.: In producer-consumer problem, producer wants to sleep till at least one buffer slot is empty - only the consumer thread can tell when a buffer slot is

How to sync SQLite database on Android phone with MySQL database on server?

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问题 I am developing an android application. I want to update the local SQLite database with MySQL database on server. I am not able to figure out that what is the most appropriate and standardized way to do so? 回答1: Create a webservice (REST is probably best) and serialize your SQLite/MySQL data and PUT/POST/GET it to/from your web service. This will give you a nice layer of abstraction in case you decide to switch from MySQL to something else server side. 回答2: You may want to take a look at