thread-safety

问题 I have a question about thread safety. From what I have been told, SimpleDateFormat is not thread safe. I was wondering what effects it would have if I use it the following way in my spring controller: private final static SimpleDateFormat dateFormat = new SimpleDateFormat("EEE MMM dd yyyy", Locale.US); Later in my of my controller functions I use it as follows: try { changedate = changedate.substring(0, 15); calcDate = dateFormat.parse(changedate); } catch (ParseException e2) { logger.error(

问题 I have a question about thread safety. From what I have been told, SimpleDateFormat is not thread safe. I was wondering what effects it would have if I use it the following way in my spring controller: private final static SimpleDateFormat dateFormat = new SimpleDateFormat("EEE MMM dd yyyy", Locale.US); Later in my of my controller functions I use it as follows: try { changedate = changedate.substring(0, 15); calcDate = dateFormat.parse(changedate); } catch (ParseException e2) { logger.error(

问题 Using Python 2.7.3 on Windows. How can I share a variable num between threads, such that, after num is squared, it is printed? I realized that I need to understand how threads work, but docs don't have much, and I haven't found anything here either.. So, could someone explain how threads work and how to share variables between 2 threads? My code (keeps printing 2 ) import threading def func1(num): while num < 100000000: num = num**2 def func2(num): while num < 100000000: print num, num = 2

问题 I want to ensure my website is capable of being hosted on the cloud in the future and also that it can handle a lot of requests. How safe are static variables? Are they unsafe because separate requests by separate users are actually sharing these static variables? Or is it because if you spread the site over threads/sharding or similar, (to handle high loads) the threads are sharing the static variables? Mainly I have helper classes, with static properties, should I change this architecture

问题 Could I write (with IndexWriter ) new documents into index while it is opened for reading (with IndexReader )? Or must I close reading before writing? Could I read/search documents (with IndexReader ) in index while it is opened for writing (with IndexWriter )? Or must I close writing before reading? Is Lucene.Net thread safely or not? Or must I write my own? 回答1: You may have any amount of readers/searchers opened at any time, but only one writer. This is enforced by a directory specific

问题 This question already has answers here : What is the difference between atomic / volatile / synchronized? (7 answers) Closed 3 months ago . I know volatile allows for visibility, AtomicInteger allows for atomicity. So if I use a volatile AtomicInteger , does it mean I don't have to use any more synchronization mechanisms? Eg. class A { private volatile AtomicInteger count; void someMethod(){ // do something if(count.get() < 10) { count.incrementAndGet(); } } Is this threadsafe? 回答1: I believe

问题 I read the ZeroMq guide and I stumbled upon the following: You MUST NOT share ØMQ sockets between threads. ØMQ sockets are not threadsafe. Technically it's possible to do this, but it demands semaphores, locks, or mutexes. This will make your application slow and fragile. The only place where it's remotely sane to share sockets between threads are in language bindings that need to do magic like garbage collection on sockets. and later on: Remember: Do not use or close sockets except in the

问题 After watching Herb Sutter's talk You Don't Know const and mutable, I wonder whether I should always define a mutex as mutable? If yes, I guess the same holds for any synchronized container (e.g., tbb::concurrent_queue )? Some background: In his talk, he stated that const == mutable == thread-safe, and std::mutex is per definition thread-safe. There is also related question about the talk, Does const mean thread-safe in C++11. Edit: Here, I found a related question (possibly a duplicate). It

问题 I've just started playing with Android Concurrency/Loopers/Handers, and I have just faced with strange anomaly. The code below doesn't block me from setting text on TextView from different Thread. TextView tv; Handler backgroundHandler; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); tv = (TextView) findViewById(R.id.sample_text); Runnable run = new Runnable() { @Override public void run() { Looper

问题 This is just a curious question. Which one is the best way to update UI from another thread. First, this one: private delegate void MyDelegateMethod(); void MyMethod() { if (unknowncontrol.InvokeRequired) { this.BeginInvoke(new MyDelegateMethod(MyMethod)); return; } unknowncontrol.property = "updating!"; } On the other hand: Invoke((System.Threading.ThreadStart)delegate() { unknowncontrol.property = "updating!"; }); Or, is there a better way to do this? Of course this is for WinForms, for WPF