locking

We have a website running .NET 2.0 and have started using the ASP.Net HttpRuntime.Cache to store the results of frequent data lookups to cut down our database access. Snippet: lock (locker) { if (HttpRuntime.Cache[cacheKey] == null) { HttpRuntime.Cache.Insert(cacheKey, GetSomeDataToCache(), null, DateTime.Today.AddDays(1), Cache.NoSlidingExpiration); } return ((SomeData)HttpRuntime.Cache[cacheKey]).Copy(); } We are pessimistically locking whenever we want to look at the cache. However, I've seen various blogs posted around the web suggesting you lock after you check the cache value instead, to

For concurrency and ensuring the integrity of the data, how would you obtain a mutual-exclusion lock for a given object? Would you need to use locking within the database, or a file, or does PHP support something like this? PHP doesn't support multithreading so there's no locking mechanism for objects. If you want to lock a file you could use flock for that. There's no need to lock database as database engines usually can handle multiple connections. Bare in mind PHP is not multithreaded, so it's unlikely you need anything like this... however, may be needed if you use shared memory, or any

How would I validate that a jpg file is a valid image file. We are having files written to a directory using FTP, but we seem to be picking up the file before it has finished writing it, creating invalid images. I need to be able to identify when it is no longer being written to. Any ideas? Easiest way might just be to write the file to a temporary directory and then move it to the real directory after the write is finished. Or you could check here . JPEG::Error [arguments: none] If the file reference remains undefined after a call to new, the file is to be considered not parseable by this

The recommended way to use a mutex for locking a critical region of code is via RAII, i.e. mutex_type mutex; { // start of critical region std::lock_guard<mutex_type> lock(mutex); // first statement in critical region // ... do critical stuff, may throw an exception } // end of critical region so that when an exception is thrown within the critical region, the mutex will still be unlocked (by the destructor of std::lock_guard ). However, this way the members mutex::lock() and mutex::unlock() are never explicitly called by user code. Q What, if any, is the major idiomatic explicit use of mutex:

I am not sure how can I solve my problem. From time to time I get the error: "The process cannot access the file 'xxxx' because it is being used by another proces". Here is my method where the error happens: private static void write_history(int index, int time_in_sec, int[] sent_resources) { string filepath = "Config\\xxx.txt"; int writing_index = 0; if (File.Exists(filepath)) { System.Threading.Thread.Sleep(5000); StreamReader reader = new StreamReader(new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.Read)); string temp = reader.ReadToEnd(); reader.Close(); for (int i = 0;

Hazelcast locks (such as http://www.hazelcast.com/docs/1.9.4/manual/multi_html/ch02s07.html ) as I understand it behave the same way as the Java concurrency primitives but across the cluster. The makes it possible to use to synchronize between thread in the local process as well as over the cluster. However, is there any way I can opt out of this behaviour? In my current project, I need a way of coordinating unique ownership of a resource across the cluster but want to aquire and release this ownership from multiple points in my application - can I do this in some way that does not involve