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  • Is there a way to efficiently yield every file in a directory containing millions of files?

    - by Josh Smeaton
    I'm aware of os.listdir, but as far as I can gather, that gets all the filenames in a directory into memory, and then returns the list. What I want, is a way to yield a filename, work on it, and then yield the next one, without reading them all into memory. Is there any way to do this? I worry about the case where filenames change, new files are added, and files are deleted using such a method. Some iterators prevent you from modifying the collection during iteration, essentially by taking a snapshot of the state of the collection at the beginning, and comparing that state on each move operation. If there is an iterator capable of yielding filenames from a path, does it raise an error if there are filesystem changes (add, remove, rename files within the iterated directory) which modify the collection? There could potentially be a few cases that could cause the iterator to fail, and it all depends on how the iterator maintains state. Using S.Lotts example: filea.txt fileb.txt filec.txt Iterator yields filea.txt. During processing, filea.txt is renamed to filey.txt and fileb.txt is renamed to filez.txt. When the iterator attempts to get the next file, if it were to use the filename filea.txt to find it's current position in order to find the next file and filea.txt is not there, what would happen? It may not be able to recover it's position in the collection. Similarly, if the iterator were to fetch fileb.txt when yielding filea.txt, it could look up the position of fileb.txt, fail, and produce an error. If the iterator instead was able to somehow maintain an index dir.get_file(0), then maintaining positional state would not be affected, but some files could be missed, as their indexes could be moved to an index 'behind' the iterator. This is all theoretical of course, since there appears to be no built-in (python) way of iterating over the files in a directory. There are some great answers below, however, that solve the problem by using queues and notifications. Edit: The OS of concern is Redhat. My use case is this: Process A is continuously writing files to a storage location. Process B (the one I'm writing), will be iterating over these files, doing some processing based on the filename, and moving the files to another location. Edit: Definition of valid: Adjective 1. Well grounded or justifiable, pertinent. (Sorry S.Lott, I couldn't resist). I've edited the paragraph in question above.

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  • JsonIgnore attributes not working in ASP.NET?

    - by Geoffrey
    I've got an object in my project with circular references. I've put [JsonIgnore] above the field like so: [JsonIgnore] public virtual Foobar ChildObject { get; set; } I'm still getting circular reference errors when I serialize the object. The only fields that do not have JsonIgnore are string fields and should not cause this. Is there something else I need to do to get JsonIgnore to work? Thanks!

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  • Does anyone know of a good guide to configure GC in Java?

    - by evilpenguin
    I'm having trouble with a JVM running an app, whose heap memory looks like a comb. It's constantly jumping from 1.5 GB to 3 GB and slowly deteriorating to higher values. I'm using G1 GC algorithm, but have no idea how to configure it. I do not have access to the code of the app I'm running and, needless to say, it's a rather large app. So, bottom line, does anyone know of a good guide to configure GC in Java?

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  • C# Saving an arraylist to a file?

    - by Zka
    I have a simple program where I would like to save an arraylist to a file, so that when the program is restarted, it loads from the file to the arraylist in memory. Is this possible in C#? Or do I need to itterate over the arraylist countaining my custom classes and in someway print them out? Any tips on a correct way to do this?

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  • how to swap array-elements to transfer the array from a column-like into a row-like representation

    - by Christian Ammer
    For example: the array a1, a2, a3, b1, b2, b3, c1, c2, c3, d1, d2, d3 represents following table a1, b1, c1, d1 a2, b2, c2, d2 a3, b3, c3, d3 now i like to bring the array into following form a1, b1, c1, d1, a2, b2, c2, d2, a3, b3, c3, d3 Does an algorithm exist, which takes the array (from the first form) and the dimensions of the table as input arguments and which transfers the array into the second form? I thougt of an algorithm which doesn't need to allocate additional memory, instead i think it should be possible to do the job with element-swap operations.

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  • What causes POCO proxy entities to only sometimes be created in Entity Framework 4.

    - by Kohan
    I have set up my POCOs and I have marked their public properties as virtual and I am successfully getting Proxies most of the time (95%) but randomly I am getting EF return some proxies and some non-proxies. Recycling the app pool when this happens will then fix this instance of the error and it will go away for an amount of time. Then it will re-occur in some other random (it seems) place. What can cause this sort of behaviour? Thanks, Kohan

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  • Fast inter-process (inter-threaded) communications IPC on large multi-cpu system.

    - by IPC
    What would be the fastest portable bi-directional communication mechanism for inter-process communication where threads from one application need to communicate to multiple threads in another application on the same computer, and the communicating threads can be on different physical CPUs). I assume that it would involve a shared memory and a circular buffer and shared synchronization mechanisms. But shared mutexes are very expensive (and there are limited number of them too) to synchronize when threads are running on different physical CPUs.

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  • state server session - cross appDomain?

    - by newone1
    When using a State server for session, are sessions still appDomain specific? So for example, I have two different IIS applications(virtual directories) on a web server, and they both point to one state server for session. The session guid from the cookie will be the same across requests from both applications, so will the same session be accessible across both of these applications? Thanks.

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  • How do I convert a System::IO::Stream^ to an LPCSTR for PlaySound?

    - by Jon Cage
    I'm trying to embed and then play back a .wav file in a C++/CLI app but all the examples I've seen which use PlaySound are in VB. I can't see how to get froma Stream^ to the LPCSTR which PlaySound requires: System::IO::Stream^ s = Assembly::GetExecutingAssembly()->GetManifestResourceStream ("Ping.wav"); LPCSTR buf = s->????; PlaySound(buf, NULL, SND_ASYNC|SND_MEMORY|SND_NOWAIT); I guess I need some sort of horrible .net memory conversion magic.

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  • If I Design a CPU Can I Get it Realized in Hardware at a Reasonable Cost?

    - by mudge
    I want to design a CPU and possibly memory and other hardware. I could do this with a hardware description language. Once I do this is it possible for me to send my designs to a manufacturer who will realize the design in hardware and send back to me the CPU(s) ? Can it be done at a reasonable cost? I want to design and make my own computer system and actually have it realized in hardware.

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  • How to create sandbox in C# for external process?

    - by SuitUp
    How to create sandbox in C# for external process? As sandbox i understand an environment for process i start from C#, that stop that process from interfering with anything else - kernel, system variables, system configuration, memory, registry, disk, hardware, location other than starting place and so on. I want place executable in one place and be sure that this place is only place that can be changed by this process. Additionaly, executable can be written in c, c++, c# etc.

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  • Accessing smart card with Java

    - by Tom Brito
    I'm trying to learn about how does Java access smart cards, due to a project analysis. I wonder if there is any kind of virtual smart card which I could use to make some tests with Java? By the way, I've read about Java Card, and looks like it is used to run Java in cards, not to smart card data access, right?

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  • Cannot .Count() on IQueryable (NHibernate)

    - by Bruno Reis
    Hello, I'm with an irritating problem. It might be something stupid, but I couldn't find out. I'm using Linq to NHibernate, and I would like to count how many items are there in a repository. Here is a very simplified definition of my repository, with the code that matters: public class Repository { private ISession session; /* ... */ public virtual IQueryable<Product> GetAll() { return session.Linq<Product>(); } } All the relevant code in the end of the question. Then, to count the items on my repository, I do something like: var total = productRepository.GetAll().Count(); The problem is that total is 0. Always. However there are items in the repository. Furthermore, I can .Get(id) any of them. My NHibernate log shows that the following query was executed: SELECT count(*) as y0_ FROM [Product] this_ WHERE not (1=1) That must be that "WHERE not (1=1)" clause the cause of this problem. What can I do to be able .Count() the items in my repository? Thanks! EDIT: Actually the repository.GetAll() code is a little bit different... and that might change something! It is actually a generic repository for Entities. Some of the entities implement also the ILogicalDeletable interface (it contains a single bool property "IsDeleted"). Just before the "return" inside the GetAll() method I check if if the Entity I'm querying implements ILogicalDeletable. public interface IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { IQueryable<TEntity> GetAll(); ... } public abstract class Repository<TEntity, TId> : IRepository<TEntity, TId> where TEntity : Entity<TEntity, TId> { public virtual IQueryable<TEntity> GetAll() { if (typeof (ILogicalDeletable).IsAssignableFrom(typeof (TEntity))) { return session.Linq<TEntity>() .Where(x => (x as ILogicalDeletable).IsDeleted == false); } else { return session.Linq<TEntity>(); } } } public interface ILogicalDeletable { bool IsDeleted {get; set;} } public Product : Entity<Product, int>, ILogicalDeletable { ... } public IProductRepository : IRepository<Product, int> {} public ProductRepository : Repository<Product, int>, IProductRepository {} Edit 2: actually the .GetAll() is always returning an empty result-set for entities that implement the ILogicalDeletable interface (ie, it ALWAYS add a WHERE NOT (1=1) clause. I think Linq to NHibernate does not like the typecast.

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  • JavaScript: How can I determine what objects are being collected by the garbage collector?

    - by shino
    I have significant garbage collection pauses. I'd like to pinpoint the objects most responsible for this collection before I try to fix the problem. I've looked at the heap snapshot on Chrome, but (correct me if I am wrong) I cannot seem to find any indicator of what is being collected, only what is taking up the most memory. Is there a way to answer this empirically, or am I limited to educated guesses?

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  • How can I use one stream and save result to many places?

    - by plasticrabbit
    I using servlet and Apache ServletFileUpload that provides stream to uploaded image. All I want to do is to store that image to db and also store resized (I using JAI) version to db. How can I achieve this without saving image to drive. As I understand stream can be read only once. So I need to store whole image in memory? Is it expensive for performance? Or there are another way?

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  • What is the meaning of this C++ Error std::length_error

    - by Janusz
    While running my program I get this Error: terminate called after throwing an instance of 'std::length_error' what(): basic_string::_S_create Abort trap I know that you can't do much without the code but I think that error is to deep in the code to copy all of it. Maybe I can figure it out if I understand what this error means. Is this a sign for an issue with reading or writing at the wrong memory address? Is there something I can do to get more information about the problem from my program?

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  • Passing a pointer to a function in objective-c

    - by Chiodo
    Hi, i've a stupid questiona about passing pointer. I've this: @interface MyClass : NSObject myobj* foo; -(void)doSomething:(myobj*)aObj; @end @implementation MyClass -(void)doSomething:(myobj*)aObj { cFuncCall(&aObj); //alloc memory and init the object } -(id)init { //init stuff... [self doSomething:foo]; // foo retun 0x0!!! } @end why foo return nil??? It should be initialized by cFuncCall!

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