concurrency

问题 I know that it is not possible to lock a ConcurrentHashMap for exclusive access. However, I cannot find why. Is it because the "Segments" which constitue CHM aren't exposed by the api? Presumably if they were, the client code could perform a "hand-over-hand" locking? Cheers 回答1: I know that it is not possible to lock a ConcurrentHashMap for exclusive access. However, I cannot find why. Simple - because it is not true. How about single instance per thread? How about synchronized methods or

问题 (The first obstacle when posting this was deciding on a good title - hope I did OK with that.) I'm slightly bewildered by how the native JavaScript Promise object behaves (tested in Chrome and Firefox in Windows 7), and whether or not they actually execute in parallel or not. I sought enlightenment here on SO, but found none as of yet. Consider this block of code: (function PromiseTester() { var counter = 0; new Promise(function(resolve) { for(var i = 0; i < 500000000; i++) counter = i;

问题 I have two threads One and Two. defined by their respective classes in the header file.I want to start the second thread when the first thread is started. creating and starting the second thread in the constructor of the first produced unexpected result. my header file "header.h" #ifndef HEADER #define HEADER #include <QtGui> class One:public QThread { public: One(); void run(); }; class Two:public QThread { public: Two(); void run(); }; #endif my class file "main.cpp" #include "header.h"

问题 I have the below code. I am using pyspark 1.2.1 with python 2.7 (cpython) for colname in shuffle_columns: colrdd = hive_context.sql('select %s from %s' % (colname, temp_table)) # zip_with_random_index is expensive colwidx = zip_with_random_index(colrdd).map(merge_index_on_row) (hive_context.applySchema(colwidx, a_schema) .registerTempTable(a_name)) The thing about this code is that it only operates on one column at a time. I have enough nodes in my cluster that I could be operating on many

问题 I am new to android programming and 've not thoroughly studied java before . I am really confused on how to use synchronized to ensure thread safety on static variables : I usually create a class named Utils which has some static functions which are most of the time needed by all my other classes. Is this the correct way of keeping repetitive code out of my classes. I always suffer from a problem with using Databases. When I create sqliteHelper class for certain Database and try to manage

问题 I followed the advice I found in this post using CountDownLatch and i'm running into a problem. I wrote up this test and ran it and my thread I created blocks when i try to synchronize on lock. private CountDownLatch lock = new CountDownLatch(1); @Test public void testBlock() { Runnable r = new Runnable() { @Override public void run() { try { synchronized(this) { this.wait(50); } } catch (InterruptedException e) { e.printStackTrace(); throw (new RuntimeException(e)); } releaseLock(); } };

问题 How to make multiple HTTP POST queries in one moment using Python? Using an external library with an example can be a good solution. 回答1: External lib? Maybe an internal one would do the trick... http://docs.python.org/library/httplib.html#examples specifically: params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0}) If you wanted to process multiple HTTP POST queries (asynchronous) you could cycle through them in a loop, opening subprocesses using subprocess.Popen . Although a better

问题 It is said, that ReentrantReadWriteLock is intended for one writer and multiple readers. Nevertheless, readers should wait until some data is present in the buffer. So, what to lock? I created concurrency objects like follows: private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock(); protected final Lock readLock = rwl.readLock(); protected final Lock writeLock = rwl.writeLock(); protected final Condition hasData = writeLock.newCondition(); now in write method I do: writeLock

问题 We are having issues to scale out our ASP.NET Web API on Azure because of our SQL Azure DB. The issue is that our Web/Business SQL Azure DB supports a maximum of 180 concurrent requests. At multiple occasions, we've hit that limit, and the following exception is thrown: Resource ID : 1. The request limit for the database is 180 and has been reached. See 'http://go.microsoft.com/fwlink/?LinkId=267637' To prevent that to happen, we explicitly set the "Max Pool Size" property of our

问题 While I am reading java.util.concurrent.locks.Condition API documentation, I see that: When waiting upon a Condition, a "spurious wakeup" is permitted to occur, in general, as a concession to the underlying platform semantics. This has little practical impact on most application programs as a Condition should always be waited upon in a loop, testing the state predicate that is being waited for. An implementation is free to remove the possibility of spurious wakeups but it is recommended that