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• Linux and I/O completion ports?

  - by someguy

  Using winsock, you can configure sockets or seperate I/O operations to "overlap". This means that calls to perform I/O are returned immediately, while the actual operations are completed asynchronously by separate worker threads. Winsock also provides "completion ports". From what I understand, a completion port acts as a multiplexer of handles (sockets). A handle can be demultiplexed if it isn't in the middle of an I/O operation, i.e. if all its I/O operations are completed. So, on to my question... does linux support completion ports or even asynchronous I/O for sockets?

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• C functions invoked as threads - Linux userland program

  - by Einar

  I'm writing a linux daemon in C which gets values from an ADC by SPI interface (ioctl). The SPI (spidev - userland) seems to be a bit unstable and freezes the daemon at random times. I need to have some better control of the calls to the functions getting the values, and I was thinking of making it as a thread which I could wait for to finish and get the return value and if it times out assume that it froze and kill it without this new thread taking down the daemon itself. Also I could do other things like resetting the ADC before restarting. Is this possible? Pseudo example of what I want to achieve: (function int get_adc_value(int adc_channel, float *value) ) pid = thread( get_adc_value(1,&value); //makes thread wait_until_finish(pid, timeout); //waits until function finishes/timesout if(timeout) kill pid, start over //if thread do not return in given time, kill it (it is frozen) else if return value sane, continue //if successful, handle return variable value and continue Thanks for any input on the matter, examples highly appreciated!

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• Fixing permissions after FTPing ASP.NET code to a Linux system

  - by dnord

  First off, I'm running Mono to run ASP.NET on Linux, but that's not the question. It appears that, every time I clear out my application directory and upload, I have to go back in and fix the permissions. What I'm doing is chmod -R -c 755 /var/www/* ...and there are two questions. What's the deal with having to do this every time I FTP? Feels flaky. Is there a better permissions set than 755? Do I want different permissions for the /bin directory? Or can I fix this all with one fell swoop of chown?

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• C / JSON Library in popular Linux distros?

  - by Tim Post

  I have a program written in C that has to input and output JSON over a local domain socket. I've found several C / JSON libraries that 'almost work' through searches. Prior to taking one of the libraries that I found .. I want to be sure that I'm not over-looking a library that is commonly found on modern Linux distros. I'd also really appreciate links to libraries that you use. Most likely, I'll just drop it in tree, unless I realize that I've over looked something widely distributed. I am tagging this as subjective because the answer that I select is the one linking to a library that works for me, that does not mean its the 'best' library. I want to take an existing array and easily convert it to a buffer that can be sent, or take a buffer and easily convert it into an allocated array. Thanks in advance!

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• Test for external undefined references in Linux

  - by Charles

  Is there a built in linux utility that I can use to test a newly compiled shared library for external undefined references? Gcc seems to be intelligent enough to check for undefined symbols in my own binary, but if the symbol is a reference to another library gcc does not check at link time. Instead I only get the message when I try to link to my new library from another program. It seems a little silly to get undefined reference messages in a library when I am compiling a different project so I want to know if I can do a check on all references internal and external when I build the library not when I link to it. Example error: make -C UnitTests debug make[1]: Entering directory `~/projects/Foo/UnitTests` g++ [ tons of objects ] -L../libbar/bin -lbar -o UnitTests libbar.so: undefined reference to `DoSomethingFromAnotherLibrary` collect2: ld returned 1 exit status make[1]: *** [~/projects/Foo/UnitTests] Error 1

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• trivial linux sound playback

  - by anon

  The classical C program is something like: int main() { fprintf(stderr, "hello world\n"); } a classical OpenGL program is: open up a window setup ortho view draw a colored triangle Now, I want to do the most basic thing for sound in Linux. I want to: 1) open up speakers 2) send a bunch of data, meant to be interpreted at 40Khz, 3) have pseakers play said data no midi, no instruments, ... just playing back raw data What is the easiest way to do this in a C program? [and what libraries; what's the equiv to OpenGL for sound?] Thanks!

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• Linux - File was deleted and then reappeared when folder was zipped

  - by davee9

  Hello, I am using Backtrack 4 Final, which is a Linux distro that is Ubuntu based. I had a directory that contained around 5 files. I deleted one of the files, which sent it to the trash. I then zipped the directory up (now containing 4 files), using this command: zip -r directory.zip directory/ When I then unzipped directory.zip, the file I deleted was in there again. I couldn't believe this, so I zipped up the directory again, and the file reappeared again but this time could not be opened because the operating system said it didn't exist or something. I don't remember the exact error, and I cannot make this happen again. Would anyone happen to know why a file that was deleted from a directory would reappear in that directory after it was zipped up? Thank you.

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• Understanding top output in Linux

  - by Rayne

  Hi, I'm trying to determine the CPU usage of a program by looking at the output from Top in Linux. I understand that %us means userspace and %sy means system/kernel etc. But say I see 100%us. Does this mean that the CPU is really only doing useful work? What if a CPU is tied up waiting for resources that are not avaliable, or cache misses, would it also show up in the %us column, or any other column? Thank you.

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• Performance Overhead of Perf Event Subsystem in Linux Kernel

  - by Bo Xiao

  Performance counters for Linux are a new kernel-based subsystem that provide a framework for all things performance analysis. It covers hardware level (CPU/PMU, Performance Monitoring Unit) features and software features (software counters, tracepoints) as well. Since 2.6.33, the kernel provide 'perf_event_create_kernel_counter' kernel api for developers to create kernel counter to collect system runtime information. What I concern most is the performance impact on overall system when tracepoint/ftrace is enabled. There are no docs I can find about them. I was once told that ftrace was implemented by dynamically patching code, will it slow the system dramatically?

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• Debug Linux kernel pre-decompression stage

  - by Shawn J. Goff

  I am trying to use GDB to debug a Linux kernel zImage before it is decompressed. The kernel is running on an ARM target and I have a JTAG debugger connected to it with a GDB server stub. The target has to load a boot loader. The boot loader reads the kernel image from flash and puts it in RAM at 0x20008000, then branches to that location. I have started GDB and connected to the remote target, then I use GDB's add-symbol-file command like so: add-symbol-file arch/arm/boot/compressed/vmlinux 0x20008000 -readnow When I set a breakpoint for that address, it does trap at the correct place - right when it branches to the kernel. However, GDB shows the wrong line from the source of arch/arm/boot/compressed/head.S. It's 4 lines behind. How can I fix this? I also have tried adding the -s section addr option to add-symbol-file with -s .start 0x20008000; this results in exactly the same problem.

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• Problem with "write" function in linux

  - by Dumitru Catalin

  I am trying to write 2 server/client programs under Linux, in which they communicate through named pipes. The problem is that sometimes when I try to write from the server into a pipe that doesn't exist anymore (the client has stopped), I get a "Resource temporarily unavailable" error and the server stops completely. I understand that this is caused by using a O_NONBLOCK parameter when opening the fifo chanel, indicating the point where the program would usually wait until it could write again in the file, but is there a way to stop this behavior, and not halt the entire program if a problem occurs (shouldn't the write command return -1 ad the program continue normally)? And another strange thing is that this error only occurs when running the programs outside the ide (eclipse). If I run both programs inside eclipse, on error the write function just returns -1 and the programs continues normally.

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• Preallocate memory for a program in Linux before it gets started

  - by Fyg

  Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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• audio stream sampling rate in linux

  - by farhan

  Im trying read and store samples from an audio microphone in linux using C/C++. Using PCM ioctls i setup the device to have a certain sampling rate say 10Khz using the SOUND_PCM_WRITE_RATE ioctl etc. The device gets setup correctly and im able to read back from the device after setup using the "read". int got = read(itsFd, b.getDataPtr(), b.sizeBytes()); The problem i have is that after setting the appropriate sampling rate i have a thread that continuously reads from /dev/dsp1 and stores these samples, but the number of samples that i get for 1 second of recording are way off the sampling rate and always orders of magnitude more than the set sampling rate. Any ideas where to begin on figuring out what might be the problem?

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• Test for undefined references in Linux

  - by Charles

  Is there a built in linux utility that I can use to test a newly compiled shared library for external undefined references? Gcc seems to be intelligent enough to check for undefined symbols in my own binary, but if the symbol is a reference to another library gcc does not check at link time. Instead I only get the message when I try to link to my new library from another program. It seems a little silly to get undefined reference messages in a library when I am compiling a different project so I want to know if I can do a check on all references internal and external when I build the library not when I link to it. Example error: make -C UnitTests debug make[1]: Entering directory `~/projects/Foo/UnitTests` g++ [ tons of objects ] -L../libbar/bin -lbar -o UnitTests libbar.so: undefined reference to `DoSomethingFromAnotherLibrary` collect2: ld returned 1 exit status make[1]: *** [~/projects/Foo/UnitTests] Error 1

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• How send html mail using linux command line

  - by Diesel Draft

  Hi, I need send mail with html format. I have only linux comand line and command "mail". Currently have used: echo "To: [email protected]" > /var/www/report.csv echo "Subject: Subject" >> /var/www/report.csv echo "Content-Type: text/html; charset=\"us-ascii\"" >> /var/www/report.csv echo "<html>" >> /var/www/report.csv mysql -u ***** -p***** -H -e "select * from users LIMIT 20" dev >> /var/www/report.csv echo "</html>" >> /var/www/report.csv mail -s "Built notification" [email protected] < /var/www/report.csv But in my mail-agent i get only plain/text.

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• How to change FPU context in signal handler (C++/Linux)

  - by Henry Fané

  I wrote a signal handler to catch FPE errors. I need to continue execution even if this happens. I receive a ucontext_t as parameter, I can change the bad operand from 0 to another value but the FPU context is still bad and I run into an infinite loop ? Does someone already manupulate the ucontext_t structure on Linux ? I finally found a way to handle these situations by clearing the status flag of ucontext_t like this: ... const long int cFPUStatusFlag = 0x3F; aContext->uc_mcontext.fpregs->sw &= ~cFPUStatusFlag; ... 0x3F is negated to put 0 in the 6 bits of the status register of the FPU (x87). Doing this implies to check for FPE exceptions after calculation.

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• Linux c++ error: undefined reference to 'dlopen'

  - by lerax

  Hi all! I work in Linux with c++ (eclipse) and want to use a library. Eclipse shows me an error: undefined reference to 'dlopen' Do you know a solution? Here is my code. #include <stdlib.h> #include <stdio.h> #include <dlfcn.h> int main(int argc, char **argv) { void *handle; double (*desk)(char*); char *error; handle = dlopen ("/lib/CEDD_LIB.so.6", RTLD_LAZY); if (!handle) { fputs (dlerror(), stderr); exit(1); } desk= dlsym(handle, "Apply"); if ((error = dlerror()) != NULL) { fputs(error, stderr); exit(1); } dlclose(handle); }

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• using Eclipse to develop for embedded Linux on a Windows host

  - by Travis

  I got a question of using Eclipse to develop for embedded Linux on a Windows host Here are now I have and where I am. 1. a Windows host that have the latest Eclipse + CDT (c/c++ development tools) installed 2. a Ubuntu host (ssh + samba installed) that contains sources and toolschain to build the project. (the windows and ubuntu hosts are sitting within one network segment (In LAN).) 3. I can use the following commands to build this project under Ubuntu. # chroot dummyroot # cd /home/project/Build # sh Build date +%Y%m%d%H%M%S 4. I am now trying to create an eclipse C++ project to achieve the goad of the step 3, but I have been stuck here for a while. any ideas of how it can be done?

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• AIO network sockets and zero-copy under Linux

  - by remyhorton

  I have been experimenting with async Linux network sockets (aio_read et al in aio.h/librt), and one thing i have been trying to find out is whether these are zero-copy or not. Pretty much all i have read so far discusses file I/O, whereas its network I/O i am interested in. AIO is a bit of a pain to use and i suspect is non-portable, so wondering whether its worth persevering with it. Zero-copy is just about the only advantage (albiet a major one for my purposes) it would have over (non-blocking) select/epoll..

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• UTF8 issues on Linux

  - by user363808

  Hi, I have some code that fetches some data from the database, database codepage is UTF8. When I run the code on a linux box, some characters come out as question marks (?) but when I run the same code on a windows server, all characters appear correctly. When I do: $ $LANG Following is returned en_SG.UTF-8 en_SG is something that doesn't look correct, it should be en_US but the latter part of the returned string is UTF-8 which is good. Is there anything else that I can look into to fix the character corruption problem?

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• malloc hangs in Linux

  - by Rahul

  I am using Linux on a 16 G with 2 quad core CPU. There are 8 processes which are doing some work (CPU intensive/network i/o). Out of which 4 have a memory leak (These are test conditions so no problem in having leaks here). Total space is occupied by all processes is around 15.4 G only 200 MB is free in system. Things are fine for some hours. But after that malloc hangs (for a process which doesn't have a memory leak). Its stuck for for more than 4 minutes (Note CPU is not 100% but io has gone up signficantly). Now there is no problem in the hanged process. (It has not corrupted the memory). What malloc is doing? (is it tryibg to defragment or builidng up swap space).I am using SUSE 10. Any pointers?

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• Linux, C++ audio capturing (just microphone) library

  - by TheOm3ga

  I'm developing a musical game, it's like a singstar but instead of singing, you have to play the recorder. It's called oFlute, and it's still in early development stage. In the game, I capture the microphone input, then run a simple FFT analysis and compare the results to typical recorder's frequencies, thus getting the played note. At the beginning, the audio library I was using was RtAudio, but I don't remember why I switched to PortAudio, which is what I'm currently using. The problem is that, from time to time, either it crashes randomly or stops capturing, like if there were no sound coming from the microphone. My question is, what's the best option to capture microphone input on Linux? I just need to open, read, and close a flow of bytes from the microphone. I've been reading this guide, and (un)surprisingly it says: I don't think that PortAudio is very good API for Unix-like operating systems. So, what do you recommend me?

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• linux's fork and system resources

  - by Dmitry Bespalov

  Suppose I have following code in linux: int main() { FILE* f = fopen("file.txt", "w"); fork(); fwrite("A", 1, 1, f); fclose(f); return 0; } What I know about fork from documentation, is that it makes the copy of current process. It copies state of the memory as well, so *f should be equal in both instances. But what happens with system resources, such as a file handle? In this example I open the file with write intentions, so only one instance can write into file, right? Which of the instances will actually write into file? Who should care further about the file handle, and call fclose() ?

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• Scheduling jobs from a web environment on Linux

  - by Anders Feder

  Hi. I am developing an application in PHP on Linux/Apache. I want to be able to schedule PHP jobs (scripts) for execution at some specific time in the future from within the application. I know that many people will recommend cron and at, but first of all I don't need recurrence (cron) and secondly and most importantly, I need the solution to be able to scale. At was not designed with race condititions in mind, and if two users try to add a job at the same time one or both may fail. It's also important that jobs are executed at their specified time, and not just 'polled' once per minute or so. Can anyone please suggest solutions for this task? Thank you.

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• [Linux] Coding a GTK+ application without window manager?

  - by ShoX

  Hi, I want to code sth. that basically works like TiVo. Switch it on, you only see the menu or an output, so no underlying OS or anything else is directly visible to the user. So I want to use Linux as base. Can you suggest a good base distribution? Can I code a frontend without having a window-manager up and running? If yes, is that possible with java-gnome or what language/gui-framework combination would you suggest? If no, what's the minimal window manager that can handle fancy menus, etc? What does it take to create video-overlays over a HD-stream? Are there some libraries I should take a look at? Thanks

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