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  • Function overloading in C

    - by Andrei Ciobanu
    Today, looking at the man page for open(), I've noticed this function is 'overloaded': int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode); I didn't thought it's possible on C. What's the 'trick' for achieving this ?

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  • pthread functions "_np" suffix

    - by osgx
    What does "_np" suffix mean here: pthread_mutex_timedlock_np or in macros PTHREAD_MUTEX_TIMED_NP Upd: From glibc2.2 enum { PTHREAD_MUTEX_TIMED_NP, PTHREAD_MUTEX_RECURSIVE_NP, PTHREAD_MUTEX_ERRORCHECK_NP, PTHREAD_MUTEX_ADAPTIVE_NP #ifdef __USE_UNIX98 , PTHREAD_MUTEX_NORMAL = PTHREAD_MUTEX_TIMED_NP, PTHREAD_MUTEX_RECURSIVE = PTHREAD_MUTEX_RECURSIVE_NP, PTHREAD_MUTEX_ERRORCHECK = PTHREAD_MUTEX_ERRORCHECK_NP, PTHREAD_MUTEX_DEFAULT = PTHREAD_MUTEX_NORMAL #endif #ifdef __USE_GNU /* For compatibility. */ , PTHREAD_MUTEX_FAST_NP = PTHREAD_MUTEX_ADAPTIVE_NP #endif }; Does defining __USE_UNIX98 change portability of _NP functions/macro?

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  • Daemonize() issues on Debian

    - by djTeller
    Hi, I'm currently writing a multi-process client and a multi-treaded server for some project i have. The server is a Daemon. In order to accomplish that, i'm using the following daemonize() code: static void daemonize(void) { pid_t pid, sid; /* already a daemon */ if ( getppid() == 1 ) return; /* Fork off the parent process */ pid = fork(); if (pid < 0) { exit(EXIT_FAILURE); } /* If we got a good PID, then we can exit the parent process. */ if (pid > 0) { exit(EXIT_SUCCESS); } /* At this point we are executing as the child process */ /* Change the file mode mask */ umask(0); /* Create a new SID for the child process */ sid = setsid(); if (sid < 0) { exit(EXIT_FAILURE); } /* Change the current working directory. This prevents the current directory from being locked; hence not being able to remove it. */ if ((chdir("/")) < 0) { exit(EXIT_FAILURE); } /* Redirect standard files to /dev/null */ freopen( "/dev/null", "r", stdin); freopen( "/dev/null", "w", stdout); freopen( "/dev/null", "w", stderr); } int main( int argc, char *argv[] ) { daemonize(); /* Now we are a daemon -- do the work for which we were paid */ return 0; } I have a strange side effect when testing the server on Debian (Ubuntu). The accept() function always fail to accept connections, the pid returned is -1 I have no idea what causing this, since in RedHat & CentOS it works well. When i remove the call to daemonize(), everything works well on Debian, when i add it back, same accept() error reproduce. I've been monitring the /proc//fd, everything looks good. Something in the daemonize() and the Debian release just doesn't seem to work. (Debian GNU/Linux 5.0, Linux 2.6.26-2-286 #1 SMP) Any idea what causing this? Thank you

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  • Does waitpid yield valid status information for a child process that has already exited?

    - by dtrebbien
    If I fork a child process, and the child process exits before the parent even calls waitpid, then is the exit status information that is set by waitpid still valid? If so, when does it become not valid; i.e., how do I ensure that I can call waitpid on the child pid and continue to get valid exit status information after an arbitrary amount of time, and how do I "clean up" (tell the OS that I am no longer interested in the exit status information for the finished child process)? I was playing around with the following code, and it appears that the exit status information is valid for at least a few seconds after the child finishes, but I do not know for how long or how to inform the OS that I won't be calling waitpid again: #include <assert.h> #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/wait.h> int main() { pid_t pid = fork(); if (pid < 0) { fprintf(stderr, "Failed to fork\n"); return EXIT_FAILURE; } else if (pid == 0) { // code for child process _exit(17); } else { // code for parent sleep(3); int status; waitpid(pid, &status, 0); waitpid(pid, &status, 0); // call `waitpid` again just to see if the first call had an effect assert(WIFEXITED(status)); assert(WEXITSTATUS(status) == 17); } return EXIT_SUCCESS; }

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  • Audio server with best API?

    - by Wintermute
    I'm a web dev, working in a small studio with a couple of other devs and some crayon-munchers (or, "designers"). Like all the best and trendiest creative studios, we have tunes. Our tunes consists of a set of speakers that whoever wants to can plug into their machine, and DJ their little socks off via iTunes, Spotify, VLC or whatever their music player of choice happens to be. Obviously, this lacks finesse. What we WANT is this: a single, dedicated machine running some sort of audio player (ideally Win-based, but a Linux flavour isn't impossible), that exposes an API. We (ie: me and the other devs) want to write a web-based client onto it, that'll let us remotely do all sorts of funky stuff like generating on-the-fly genre-based playlists, and voting for tracks, and making tea. My question - and please forgive me if this isn't the place for such a question, I was going to ask on Stackoverflow but that didn't seem right either - is this: what's the best player to start with? What can do all of this? I know VLC can function as a streaming server, but know nothing of any API it may have. I'd rather chop my pinky off than use iTunes, but if it does what we want, then... Anyhow, thanks for reading. All comments and suggestions gratefully received.

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  • What is the best way to manage unix process from java?

    - by erotsppa
    I'm looking for some simple tasks like listing all the running process of a user, or kill a particular process by pid etc. Basic unix process management from Java. Is there a library out there that is relatively mature and documented? I could run a external command from the JVM and then parse the standard output/error but that seems like a lot of work and not robust at all. Any suggestions?

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  • Are there any platforms where using structure copy on an fd_set (for select() or pselect()) causes p

    - by Jonathan Leffler
    The select() and pselect() system calls modify their arguments (the 'struct fd_set *' arguments), so the input value tells the system which file descriptors to check and the return values tell the programmer which file descriptors are currently usable. If you are going to call them repeatedly for the same set of file descriptors, you need to ensure that you have a fresh copy of the descriptors for each call. The obvious way to do that is to use a structure copy: struct fd_set ref_set_rd; struct fd_set ref_set_wr; struct fd_set ref_set_er; ... ...code to set the reference fd_set_xx values... ... while (!done) { struct fd_set act_set_rd = ref_set_rd; struct fd_set act_set_wr = ref_set_wr; struct fd_set act_set_er = ref_set_er; int bits_set = select(max_fd, &act_set_rd, &act_set_wr, &act_set_er, &timeout); if (bits_set > 0) { ...process the output values of act_set_xx... } } My question: Are there any platforms where it is not safe to do a structure copy of the struct fd_set values as shown? I'm concerned lest there be hidden memory allocation or anything unexpected like that. (There are macros/functions FD_SET(), FD_CLR(), FD_ZERO() and FD_ISSET() to mask the internals from the application.) I can see that MacOS X (Darwin) is safe; other BSD-based systems are likely to be safe, therefore. You can help by documenting other systems that you know are safe in your answers. (I do have minor concerns about how well the struct fd_set would work with more than 8192 open file descriptors - the default maximum number of open files is only 256, but the maximum number is 'unlimited'. Also, since the structures are 1 KB, the copying code is not dreadfully efficient, but then running through a list of file descriptors to recreate the input mask on each cycle is not necessarily efficient either. Maybe you can't do select() when you have that many file descriptors open, though that is when you are most likely to need the functionality.) There's a related SO question - asking about 'poll() vs select()' which addresses a different set of issues from this question.

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  • What the best approach to iterate and "store" files over a directory in C (Linux) ?

    - by Andrei Ciobanu
    I have written a function that checks if to files are duplicates or not. This function signature is: int check_dup_memmap(char *f1_name, char *f2_name) It returns: (-1) - If something went wrong; (0) - If the two files are similar; (+1) - If the two files are different; The next step is to write a function that iterates through all the files in a certain directory,apply the previous function, and gives a report on every existing duplicates. Initially I've thought to write a function that generates a file with all the filenames in a certain directory and then, read that file again and gain and compare every two files. Here is that version of the function, that gets all the filenames in a certain directory. void *build_dir_tree(char *dirname, FILE *f) { DIR *cdir = NULL; struct dirent *ent = NULL; struct stat buf; if(f == NULL){ fprintf(stderr, "NULL file submitted. [build_dir_tree].\n"); exit(-1); } if(dirname == NULL){ fprintf(stderr, "NULL dirname submitted. [build_dir_tree].\n"); exit(-1); } if((cdir = opendir(dirname)) == NULL){ char emsg[MFILE_LEN]; sprintf(emsg, "Cannot open dir: %s [build_dir_tree]\t",dirname); perror(emsg); } chdir(dirname); while ((ent = readdir(cdir)) != NULL) { lstat(ent->d_name, &buf); if (S_ISDIR(buf.st_mode)) { if (strcmp(".", ent->d_name) == 0 || strcmp("..", ent->d_name) == 0) { continue; } build_dir_tree(ent->d_name, f); } else{ fprintf(f, "/%s/%s\n",util_get_cwd(),ent->d_name); } } chdir(".."); closedir(cdir); } Still I consider this approach a little inefficient, as I have to parse the file again and again. In your opinion what are other approaches should I follow: Write a datastructure and hold the files instead of writing them in the file ? I think for a directory with a lot of files, the memory will become very fragmented. Hold all the filenames in auto-expanding array, so that I can easy access every file by their index, because they will in a contiguous memory location. Map this file in memory using mmap() ? But mmap may fail, as the file gets to big. Any opinions on this. I want to choose the most efficient path, and access as few resources as possible. This is the requirement of the program... EDIT: Is there a way to get the numbers of files in a certain directory, without iterating through it ?

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  • Creating a virtual, data-driven section of a Wordpress-powered site

    - by lgomez
    Hello all, I want to create a plugin for wordpress to automatically serve pages containing data pulled from a provider's API. The API returns one or more records containing data for that record and I simply want to have the plugin intercept the request, call the API with parameters pulled from the request URI and display the data using a template that I can either let them upload to the server or let them copy and paste into the plugins admin settings. For example, I may want one of my wordpress installations to show products pulled from such an API under the url "example.com/products". The plugin would catch that request, extract the variables from the URL, call the API and render the template with the returned results. I'd like to avoid requiring editing the .htaccess file like some caching plugins do. Some of the admins of these pages won't know how to do that or simply won't have access to the .htaccess file. Thanks!

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  • What can cause a spontaneous EPIPE error without either end calling close() or crashing?

    - by Hongli
    I have an application that consists of two processes (let's call them A and B), connected to each other through Unix domain sockets. Most of the time it works fine, but some users report the following behavior: A sends a request to B. This works. A now starts reading the reply from B. B sends a reply to A. The corresponding write() call returns an EPIPE error, and as a result B close() the socket. However, A did not close() the socket, nor did it crash. A's read() call returns 0, indicating end-of-file. A thinks that B prematurely closed the connection. Users have also reported variations of this behavior, e.g.: A sends a request to B. This works partially, but before the entire request is sent A's write() call returns EPIPE, and as a result A close() the socket. However B did not close() the socket, nor did it crash. B reads a partial request and then suddenly gets an EOF. The problem is I cannot reproduce this behavior locally at all. I've tried OS X and Linux. The users are on a variety of systems, mostly OS X and Linux. Things that I've already tried and considered: Double close() bugs (close() is called twice on the same file descriptor): probably not as that would result in EBADF errors, but I haven't seen them. Increasing the maximum file descriptor limit. One user reported that this worked for him, the rest reported that it did not. What else can possibly cause behavior like this? I know for certain that neither A nor B close() the socket prematurely, and I know for certain that neither of them have crashed because both A and B were able to report the error. It is as if the kernel suddenly decided to pull the plug from the socket for some reason.

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  • Multithreading with STL container

    - by Steven
    I have an unordered map which stores a pointer of objects. I am not sure whether I am doing the correct thing to maintain the thread safety. typedef std::unordered_map<string, classA*>MAP1; MAP1 map1; pthread_mutex_lock(&mutexA) if(map1.find(id) != map1.end()) { pthread_mutex_unlock(&mutexA); //already exist, not adding items } else { classA* obj1 = new classA; map1[id] = obj1; obj1->obtainMutex(); //Should I create a mutex for each object so that I could obtain mutex when I am going to update fields for obj1? pthread_mutex_unlock(&mutexA); //release mutex for unordered_map so that other threads could access other object obj1->field1 = 1; performOperation(obj1); //takes some time obj1->releaseMutex(); //release mutex after updating obj1 }

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  • Checking if a file is a directory or just a file.

    - by Jookia
    I'm writing a program to check if something is a file or is a directory. Is there a better way to do it than this? #include <stdio.h> #include <sys/types.h> #include <dirent.h> #include <errno.h> int isFile(const char* name) { DIR* directory = opendir(name); if(directory != NULL) { closedir(directory); return 0; } if(errno == ENOTDIR) { return 1; } return -1; } int main(void) { const char* file = "./testFile"; const char* directory = "./"; printf("Is %s a file? %s.\n", file, ((isFile(file) == 1) ? "Yes" : "No")); printf("Is %s a directory? %s.\n", directory, ((isFile(directory) == 0) ? "Yes" : "No")); return 0; }

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  • getopt implicit declaration in Solaris?

    - by Steven
    In Solaris, gcc gives me implicit declaration of function `getopt' when compiling #include <unistd.h> #include <stdlib.h> int main(int argc, char *argv[]) { getopt(1,argv,""); return 0; } The man page for getopt says something about including unistd.h or stdio.h, however even though I'm inluding both I still get this warning. Is this normal? Is using functions that aren't explicitly declared common in Unix development?

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  • How to change PHP's eregi to preg_match

    - by jasondavis
    I need help, below is a small VERY basic regex to somewhat validate an email, I do realize it does not work the greatest but for my needs it is ok for now. It currently uses PHP's eregi function which php.net says is now a depreciated function and I should use preg_match instead, simply replacing erei with preg_match does not work, can someone show me how to make it work? function validate_email($email) { if (!eregi("^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$", $email)) { echo 'bad email'; } else { echo 'good email'; } } function validate_email($email) { if (!preg_match("^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$", $email)) { echo 'bad email'; } else { echo 'good email'; } }

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  • Force blocking read after EAGAIN?

    - by Daniel Trebbien
    I have a file descriptor that is open for reading which may be non-blocking. What I need to do is simply read all data until reaching EOF and write that data to a writable file descriptor. As the process that performs this copying is not "aware" of anything that is going on around it, I don't think that I can do something useful while waiting for data, and I don't want to use a while loop (while errno is not EAGAIN) because I think that it would be wasteful. Is there a way to block or otherwise suspend execution of the copying process until data becomes available?

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  • pthread_join from a signal handler

    - by liv2hak
    I have a capture program which in addition do capturing data and writing it into a file also prints some statistics.The function that prints the statistics static void* report(void) { /*Print statistics*/ } is called roughly every second using an ALARM that expires every second.So The program is like void capture_program() { pthread_t report_thread while(!exit_now) { if(pthread_create(&report_thread,NULL,report,NULL)){ fprintf(stderr,"Error creating reporting thread! \n"); } /* Capturing code -------------- -------------- */ if(doreport) usleep(5); } } void *report(void *param) { while(true) { if(doreport) { doreport = 0 //access some register from hardware usleep(5) } } } The expiry of the timer sets the doreport flag.If this flag is set report() is called which clears the flag.I am using usleep to alternate between two threads in the program.This seems to work fine. I also have a signal handler to handle SIGINT (i.e CTRL+C) static void anysig(int sig) { if (sig != SIGINT) dagutil_set_signal_handler(SIG_DFL); /* Tell the main loop to exit */ exit_now = 1; return; } My question: 1) Is it safe to call pthread_join from inside the signal handler? 2) Should I use exit_now flag for the report thread as well?

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  • Is O_LARGEFILE needed just to write a large file?

    - by Daniel Trebbien
    Is the O_LARGEFILE flag needed if all that I want to do is write a large file (O_WRONLY) or append to a large file (O_APPEND | O_WRONLY)? From a thread that I read titled "Cannot write 2gb index file" on the CLucene-dev mailing list, it appears that O_LARGEFILE might be needed to write large files, but participants in that discussion are using O_RDWR, not O_WRONLY, so I am not sure.

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  • Why can't a bind linux service to the loop-back only?

    - by Jon Trauntvein
    I am writing a server application that will provide a service on an ephemeral port that I only want accessible on the loopback interface. In order to do this, I am writing code like the following: struct sockaddr_in bind_addr; memset(&bind_addr,0,sizeof(bind_addr)); bind_addr.sin_family = AF_INET; bind_addr.sin_port = 0; bind_addr.sin_addr.s_addr = htonl(inet_addr("127.0.0.1")); rcd = ::bind( socket_handle, reinterpret_cast<struct sockaddr *>(&bind_addr), sizeof(bind_addr)); The return value for this call to bind() is -1 and the value of errno is 99 (Cannot assign requested address). Is this failing because inet_addr() already returns its result in network order or is there some other reason?

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  • Specific issue on data pump API in oracle

    - by Median Hilal
    I have a client/server architecture. Using an Oracle dbms on the database server side. I need to perform a user-triggered (from client side) backup of the database, where the best way to perform that is using a stored procedure on the server side which the client may call, as the client has no oracle tools to perform the backup. I've searched thorough inside available solutions and have found that using a stored procedure is the best way. Well, then I found that using oracle data pump API is the best way to use inside a PL/SQl stored procedure. My specific questions about the API are... I would like to ask about two issues ... ---- The first ----- the detach function to detach the handler, is it necessary to be used at the end of the procedure? and what if I don't use it? I read the Oracle documentation but I didn't get their point, they say it doesn't terminate the job but indicates that the user is not interested in it, an when I use detach at the end of my procedure the exported .dmp file disappears. ---- The second ----- to perform a user (client side) triggered back up as the modification are only to the data, I used TABLE parameter for the export operation. But the version parameter... what should it be? I also read the documentation but couldn't determine what I need (LATEST or COMPATIBLE) ? Thanks

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  • Lock a mutex multiple times in the same thread

    - by Megacan
    Hi, I'm developing an application on an embedded linux OS (uClinux) and I need to be able to lock the mutex more than once (by the same thread). I have a mutex and a mutexattr defined and initialized as follows: pthread_mutexattr_t waiting_barcode_mutexattr; pthread_mutex_t waiting_barcode_mutex; pthread_mutexattr_init(&waiting_barcode_mutexattr); pthread_mutexattr_settype(&waiting_barcode_mutexattr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init(&waiting_barcode_mutex, &waiting_barcode_mutexattr); But when I try to acquire the lock twice it blocks on the second lock: pthread_mutex_lock(&waiting_barcode_mutex); pthread_mutex_lock(&waiting_barcode_mutex); Am I initializing it wrong or is there a better way of accomplishing the same? Thanks in advance.

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  • Is there a c++ library that provides functionality to execute an external program and read its outpu

    - by BD at Rivenhill
    Basically, I'm looking for something that will allow me to replicate the following Perl code: my $fh = new FileHandle; $fh->open("foo |"); while (<$fh>) { # Do something with this line of data. } This is in the context of Linux, so a library that is specific to Windows will not help. I know how to write a program that does fork/exec/dup2 and all that basic shell-type jazz, but there are some fiddly details involving terminals that I don't feel like messing around with (and I don't have a copy of "Advanced Programming in the UNIX Environment" or a similar reference handy), so I'm hoping that someone has already solved this problem.

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