concurrency

问题 I have List of N items and I want to divide this List in a sequential manner between a fixed number of threads . By sequential I mean, I want to pass 1 to N/4 to first thread , N/4 + 1 to N/2 to second thread and N/2+1 to N to third thread , Now once all the threads have finished their work, I want to notify to main thread to send some message that all the processing has been completed. What I have done so far now is that I have implemented ExecutorService I did something like this

问题 I am writing an Android app which communicates with a PHP backend. The backend db is SQLite 3. The problem is, I am getting this error intermittently PHP Warning: SQLite3::prepare(): Unable to prepare statement: 5, database is locked . I am opening a connection to the database in each PHP file and closing it when the script finishes. I think the problem is that one script locked the database file while writing to it and the second script was trying to access it, which failed. One way of

问题 I have many threads that concurrently read the same file(entirely about 100M), and only one thread to update the file. I want to map the file in memory to reduce FILE I/O. How can this be done in Java? I basically have considered the following 2 methods: with byte array to store the file, and each time create ByteArrayInputStream to read the buffer when multi-thread read. with NIO to get one file channel, synchronized the channel to read from the MappedByteBuffer for multi-thread read. I'm

问题 I have many threads that concurrently read the same file(entirely about 100M), and only one thread to update the file. I want to map the file in memory to reduce FILE I/O. How can this be done in Java? I basically have considered the following 2 methods: with byte array to store the file, and each time create ByteArrayInputStream to read the buffer when multi-thread read. with NIO to get one file channel, synchronized the channel to read from the MappedByteBuffer for multi-thread read. I'm

问题 Assume we have an IO action such as lookupStuff :: InputType -> IO OutputType which could be something simple such as DNS lookup, or some web-service call against a time-invariant data. Let's assume that: The operation never throws any exception and/or never diverges If it wasn't for the IO monad, the function would be pure, i.e. the result is always the same for equal input parameters The action is reentrant, i.e. it can be called from multiple threads at the same time safely. The

问题 I was trying to make an http proxy using BaseHttpServer which is based on SocketServer which got 2 asynchronous Mixins (ThreadingMixIn and ForkingMixIn) the problem with those two that they work on each request (allocate a new thread or fork a new subprocess for each request) is there a Mixin that utilize a pool of let's say 4 subprocesses and 40 threads in each so requests get handled by those already created threads ? because this would be a big performance gain and I guess it would save

问题 I was trying to make an http proxy using BaseHttpServer which is based on SocketServer which got 2 asynchronous Mixins (ThreadingMixIn and ForkingMixIn) the problem with those two that they work on each request (allocate a new thread or fork a new subprocess for each request) is there a Mixin that utilize a pool of let's say 4 subprocesses and 40 threads in each so requests get handled by those already created threads ? because this would be a big performance gain and I guess it would save

问题 I haven't used GCD or much threading in my apps but I've run into a situation where I need to run a method or two off another thread. Once this method completes I need to call another method using the main thread from a callback. I've been searching around to see how to detect when a thread has finished the operation but still not too clear on the subject. I created a test app and just used the viewDidLoad method for a quick example. - (void)viewDidLoad { [super viewDidLoad]; // Do any

问题 I'm doing some proof-of-concept work for a fairly complex video game I'd like to write in Haskell using the HOpenGL library. I started by writing a module that implements client-server event based communication. My problem appears when I try to hook it up to a simple program to draw clicks on the screen. The event library uses a list of TChans made into a priority queue for communication. It returns an "out" queue and an "in" queue corresponding to server-bound and client-bound messages.

问题 What does the join method do? As in: def thread = Thread.start { println "new thread" } thread.join() This code works fine even without the join statement. 回答1: The same as it does in Java - it causes the thread that called join to block until the thread represented by the Thread object on which join was called has terminated. You can see the difference if you make the main thread do something else (e.g. a println ) after spawning the new thread. def thread = Thread.start { sleep(2000)