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  • Sync Vs. Async Sockets Performance in C#

    - by Michael Covelli
    Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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  • OperationalError "unable to open database file" processing query results with SQLAlchemy and SQLite3

    - by Peter
    I'm running into this little problem that I hope is just a dumb user error. It looks like some sort of a size limit with a query to a SQLite database. I managed to reproduce the issue with an in-memory DB and a simple script shown below. I can make it work by either reducing the number of records in the DB; or by reducing the size of each record; or by dropping the order_by() call. I am using Python 2.5.5 and SQLAlchemy 0.6.0 in a Cygwin environment. Thanks! #!/usr/bin/python from sqlalchemy.orm import sessionmaker import sqlalchemy import sqlalchemy.orm class Person(object): def __init__(self, name): self.name = name engine = sqlalchemy.create_engine('sqlite:///:memory:') Session = sessionmaker(bind=engine) metadata = sqlalchemy.schema.MetaData(bind=engine) person_table = sqlalchemy.Table('person', metadata, sqlalchemy.Column('id', sqlalchemy.types.Integer, primary_key=True), sqlalchemy.Column('name', sqlalchemy.types.String)) metadata.create_all(engine) sqlalchemy.orm.mapper(Person, person_table) session = Session() session.add_all([Person("012345678901234567890123456789012") for i in range(5000)]) session.commit() persons = session.query(Person).order_by(Person.name).all() print "count =", len(persons) session.close() The all() call to the query result fails with the OperationalError exception: Traceback (most recent call last): File "./stress.py", line 27, in <module> persons = session.query(Person).order_by(Person.name).all() File "/usr/lib/python2.5/site-packages/sqlalchemy/orm/query.py", line 1343, in all return list(self) File "/usr/lib/python2.5/site-packages/sqlalchemy/orm/query.py", line 1451, in __iter__ return self._execute_and_instances(context) File "/usr/lib/python2.5/site-packages/sqlalchemy/orm/query.py", line 1456, in _execute_and_instances mapper=self._mapper_zero_or_none()) File "/usr/lib/python2.5/site-packages/sqlalchemy/orm/session.py", line 737, in execute clause, params or {}) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/base.py", line 1109, in execute return Connection.executors[c](self, object, multiparams, params) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/base.py", line 1186, in _execute_clauseelement return self.__execute_context(context) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/base.py", line 1215, in __execute_context context.parameters[0], context=context) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/base.py", line 1284, in _cursor_execute self._handle_dbapi_exception(e, statement, parameters, cursor, context) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/base.py", line 1282, in _cursor_execute self.dialect.do_execute(cursor, statement, parameters, context=context) File "/usr/lib/python2.5/site-packages/sqlalchemy/engine/default.py", line 277, in do_execute cursor.execute(statement, parameters) sqlalchemy.exc.OperationalError: (OperationalError) unable to open database file u'SELECT person.id AS person_id, person.name AS person_name \nFROM person ORDER BY person.name' ()

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  • SQLSTATE 08001 error

    - by Joseph
    Hi all OUR SQL Server 2008 got freeze.and not able to connect the databse and we restrted the server(windows 2008). Even we were not able to login windows(Restrted via HP ILO). ANybody face this issue?and have a resolution. [165] ODBC Error: 0, Login timeout expired [SQLSTATE HYT00] [298] SQLServer Error: 258, Shared Memory Provider: Timeout error [258]. [SQLSTATE 08001] [382] Logon to server '(local)' failed (ConnUpdateJobActivity_NextScheduledRunDate) the above three error we got this time thanks in advance

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  • c# write big files to blob sqlite

    - by brizjin-gmail-com
    I have c# application which write files to sqlite database. It uses entity fraemwork for modeling data. Write file to blob (entity byte[] varible) with this line: row.file = System.IO.File.ReadAllBytes(file_to_load.FileName); //row.file is type byte[] //row is entity class table All work correctly when files size is less. When size more 300Mb app throw exception: Exception of type 'System.OutOfMemoryException' was thrown. How I can write to blob direct, without memory varibles?

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  • how caching is implemented using PHP GD

    - by christian
    I want to cache the images of my gallery. Generating images every pages load using GD uses a lot of memory, So I am planning to create a cache image for the images generated by php script done with GD. What will be the best thing to create cache?

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  • How to build OpenSSL in release mode with symbols?

    - by twk
    I generally build my openssl libs by doing this: perl Configure VC-WIN32 ms\do_masm nmake -f ms\ntdll.mak nmake -f ms\ntdll.mak test For debugging minidumps, I'd like to get a pdb file for the 2 dlls (while still building them in "release" mode). I've added /Zi to the CFLAGS part of ms\ntdll.mak, but I still get "Binary was not built with debug information" when I look at the in-memory modules in the visual studio debugger. Am I missing a step? Thanks

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  • Restoring/Restarting a java daemon from crash

    - by Ashish
    Hello, I am running a java app as daemon on a linux machine using a customized shell script. Since I am new to java and linux, I want to know is it possible that the app itself resurrects itself(just like restart) and recovers from cases like app crashing, unhandled exceptions or out of memory etc. thanks in advance Ashish Sharma

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  • Is dealloc method called in presentModalViewController when dismiss the controller.

    - by Madan Mohan
    Hi Guys, here the following code is used to view the present modal view controller. [[self navigationController] presentModalViewController:doctorListViewNavigationController animated:YES]; code for dismiss the ModalViewController. -(void)closeAction { [[self navigationController] dismissModalViewControllerAnimated:YES]; } My problem is the dealloc method is not called then I am getting memory issue problems like object allocations, leaks.. (void)dealloc { [doctorList release]; [myTableView release]; [super dealloc]; }

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  • UINavigationController crash because of pushing and poping UIViewControllers

    - by Wayne Lo
    My question is related to my discovery of a reason for UINavigationController to crash. So I will tell you about the discovery first. Please bare with me. The issue: I have a UINavigationController as as subview of UIWindow, a rootViewController class and a custom MyViewController class. The following steps will get a Exc_Bad_Access, 100% reproducible.: [myNaviationController pushViewController:myViewController_1stInstance animated:YES]; [myNaviationController pushViewController:myViewController_2ndInstance animated:YES]; Hit the left back tapBarItem twice (pop out two of the myViewController instances) to show the rootViewController. After a painful 1/2 day of try and error, I finally figure out the answer but also raise a question. The Solutio: I declared many objects in the .m file as a lazy way of declaring private variables to avoid cluttering the .h file. For instance, #impoart "MyViewController.h" NSMutableString*variable1; @implement ... -(id)init { ... varialbe1=[[NSMutableString alloc] init]; ... } -(void)dealloc { [variable1 release]; } For some reasons, the iphone OS may loose track of these "lazy private" variables memory allocation when myViewController_1stInstance's view is unloaded (but still in the navigation controller's stacks) after loading the view of myViewController_2ndInstance. The first time to tap the back tapBarItem is ok since myViewController_2ndInstance'view is still loaded. But the 2nd tap on the back tapBarItem gave me hell because it tried to dealloc the 2nd instance. Executing [variable release] resulted in Exc_Bad_Access because it pointed randomly (loose pointer). To fix this problem is simple, declare variable1 as a @private in the .h file. Here is my Question: I have been using the "lazy private" variables for quite some time without any issues until they are involved in UINavigationController. Is this a bug in iPhone OS? Or there is a fundamental misunderstanding on my part about Objective C? Please help.

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  • How to update a user created Bitmap in the Windows API

    - by gamernb
    In my code I quickly generate images on the fly, and I want to display them as quickly as possible. So the first time I create my image, I create a new BITMAP, but instead of deleting the old one and creating a new one for every subsequent image, I just want to copy my data back into the existing one. Here is my code to do both the initial creation and the updating. The creation works just fine, but the updating one doesn't work. BITMAPINFO bi; HBITMAP Frame::CreateBitmap(HWND hwnd, int tol1, int tol2, bool useWhite, bool useBackground) { ZeroMemory(&bi.bmiHeader, sizeof(BITMAPINFOHEADER)); bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); bi.bmiHeader.biWidth = width; bi.bmiHeader.biHeight = height; bi.bmiHeader.biPlanes = 1; bi.bmiHeader.biBitCount = 24; bi.bmiHeader.biCompression = BI_RGB; ZeroMemory(bi.bmiColors, sizeof(RGBQUAD)); // Allocate memory for bitmap bits int size = height * width; Pixel* newPixels = new Pixel[size]; // Recompute the output //memcpy(newPixels, pixels, size*3); ComputeOutput(newPixels, tol1, tol2, useWhite, useBackground); HBITMAP bitmap = CreateDIBitmap(GetDC(hwnd), &bi.bmiHeader, CBM_INIT, newPixels, &bi, DIB_RGB_COLORS); delete newPixels; return bitmap; } and void Frame::UpdateBitmap(HWND hwnd, HBITMAP bitmap, int tol1, int tol2, bool useWhite, bool useBackground) { ZeroMemory(&bi.bmiHeader, sizeof(BITMAPINFOHEADER)); bi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); HDC hdc = GetDC(hwnd); if(!GetDIBits(hdc, bitmap, 0, bi.bmiHeader.biHeight, NULL, &bi, DIB_RGB_COLORS)) MessageBox(NULL, "Can't get base image info!", "Error!", MB_ICONEXCLAMATION | MB_OK); // Allocate memory for bitmap bits int size = height * width; Pixel* newPixels = new Pixel[size]; // Recompute the output //memcpy(newPixels, pixels, size*3); ComputeOutput(newPixels, tol1, tol2, useWhite, useBackground); // Push back to windows if(!SetDIBits(hdc, bitmap, 0, bi.bmiHeader.biHeight, newPixels, &bi, DIB_RGB_COLORS)) MessageBox(NULL, "Can't set pixel data!", "Error!", MB_ICONEXCLAMATION | MB_OK); delete newPixels; } where the Pixel struct is just this: struct Pixel { unsigned char b, g, r; }; Why does my update function not work. I always get the MessageBox for "Can't set pixel data!" I used code similar to this when I was loading in the original bitmap from file, then editing the data, but now when I manually create it, it doesn't work.

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  • Huge anon blocks in pmap

    - by Parik
    I am doing a pmap on a tomcat process and I am seeing some huge anon blocks. From what I read anon blocks are used for thread stacks and for JNI. I have a very moderate thread count. How can I go about finding out what is causing these huge anon blocks? 00000000ee0d0000 26752K rwx-- [ anon ] 00000000efaf0000 33792K rwx-- [ anon ] 00000000f1bf0000 25856K rwx-- [ anon ] 00000000f3530000 39680K rwx-- [ anon ] ( on a side note is pmap the correct way to measure how much memory is allocated to tomcat?)

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  • Java OutOfMemory error in filter

    - by The Machine
    I get a java.lang.outOfMemoryError exception, while writing a big file to the servletOutputStream. Every response is by default wrapped using a ehcache.constructs.web.filter Object for GZIP compression. And as per the logs, the exception is thrown in the Filter object. Is there a way to increase the available memory so, that the outOfMemoryError Exception does not occur ?

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  • what type of bug causes a program to slowly use more processor power and all of a sudden go to 100%?

    - by reinier
    Hi, I was hoping to get some good ideas as to what might be causing a really nasty bug. This is a program which is transmitting data over a socket, and also receives messages back. I could explain lots more, but I don't think this will help here. I'm just searching for hypothetical problems which can cause the following behaviour: program runs processor time slowly accumulates (till around 60%) all of a sudden (could be after 30 but also after 60 seconds) the processor time shoots to 100%. the program halts completely In my syslog it always ends on one line with a memory allocation (something similar to: myArray = new byte[16384]) in the same thread. now here is the weird part: if I set the debugger anywhere...it immediately stops on that line. So just the act of setting a breakpoint, made the thread continue (it wasn't running since I saw no log output anymore) I was thinking 'deadlock' but that would not cause 100% processor power. If anything, the opposite. Also, setting a breakpoint would not cause a deadlock to end. anyone else a theoretical suggestion as to what kind of 'construct' might cause this effect? (apart from 'bad programming') ;^) thanks EDIT: I just noticed.... by setting the sendspeed slower, the problem shows itself much later than expected. I would think around the same amount of packets send...but no the amount of packets send is much higher this way before it has the same problem.

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  • does Entity Framework have a caching mechanism like DataSet/DataTables have?

    - by Greg
    Hi, does Entity Framework have a caching mechanism like DataSet/DataTables have? In other words if you start using EF is it really just a way to easily get data in/out of the database without providing an additional caching layer like DataSet/DataTables did where you have an in-memory representation (on-line/off-line) and which at some point you could say to "persist all changes to database"

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  • Stream multiple files in _one_ ASIHTTPRequest

    - by Snej
    What is best practice to stream multiple files in one ASIHTTPRequest? Right now, for one file I use: .... ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:someUrl]; [request setShouldStreamPostDataFromDisk:YES]; [request appendPostDataFromFile:someFilePath]; [request startSynchronous]; How to stream multiple files without placing all files in memory before transmission?

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  • Java without gc - io

    - by Dan
    Hi Guys I would like to run a Java program with garbage collection switched off. Managing memory in my own code is not so difficult. However the program needs quite a lot of I/O. Is there any way (short of using JNI for all I/O operations) that I could achieve this using pure Java? Thanks Daniel

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  • Looking for a lock-free RT-safe single-reader single-writer structure

    - by moala
    Hi, I'm looking for a lock-free design conforming to these requisites: a single writer writes into a structure and a single reader reads from this structure (this structure exists already and is safe for simultaneous read/write) but at some time, the structure needs to be changed by the writer, which then initialises, switches and writes into a new structure (of the same type but with new content) and at the next time the reader reads, it switches to this new structure (if the writer multiply switches to a new lock-free structure, the reader discards these structures, ignoring their data). The structures must be reused, i.e. no heap memory allocation/free is allowed during write/read/switch operation, for RT purposes. I have currently implemented a ringbuffer containing multiple instances of these structures; but this implementation suffers from the fact that when the writer has used all the structures present in the ringbuffer, there is no more place to change from structure... But the rest of the ringbuffer contains some data which don't have to be read by the reader but can't be re-used by the writer. As a consequence, the ringbuffer does not fit this purpose. Any idea (name or pseudo-implementation) of a lock-free design? Thanks for having considered this problem.

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