I have a simple program that listens to a socket. Everything goes fine except when the connection is lost in while(1) cycle. In this case the program falls into read from socket for many times without result. How can I detect a disconnected client in while(1) cycle? Answer Change: To: Also, your code mishandles the case where the first byte
Tag: c++
Why can only async-signal-safe functions be called from signal handlers safely?
I am still a little confused as to why exactly it is unsafe to receive a signal and call a non async safe function from within that signal handler. Could someone explain the reasoning behind this and possibly try and give me some references that I can follow to read up more on this myself? In other words I am
How to invoke scull_open() in user-space, where scull_open is defined in scull kernel driver
I am newbie to Linux device driver programming. I am just trying to use the scull driver which is explained in Linux Device Drivers. Would like to invoke the scull_open() from user-space for write/read or close operations. Currently I’m able to insert the scull module successfully using insmod and got the major number too. I also got the dev node
Time spends in CPU faster than in reality
I am wondering why my entire application runs in less than 8 seconds while the time obtained from clock_gettime is 19.3468 seconds which is more than two times as much as what happens in reality. Where is the problem from? Update: I am not using any OpenMP explicitly. Answer CLOCK_MONOTONIC should be used if you want to measure total elapsed
C segmentation fault on linux with strncmp
This works (‘Y’ must be single quotes): This gives segmentation fault: strncmp must be going off the deep end but not sure why since I’m passing a casted toupper() as (char *). Without the casting, same error. FYI user_input() is (N.B. vars are global): Thank you. Answer The return value of toupper is another character, not a pointer to a
Implement a similar module_init as Linux kernel, but meet some trouble in ld script
I like the linux kernel module_init function very much, I would like to implement the same function for my user space applications. I try to modify the linker script to do this: 1, copy a x86-64 standard ld script 2, add my customized section 3, put the init function pointer into moudle_init section 4, compile the app with a customized
POSIX message queue – Does it still exists after reboot?
On linux, wrote a simple program to create a POSIX message queue, and send a msg to it, after the process terminated, it seems the msg is still there. The questions are: Does the msg still there after reboot? If it exists, then it’s on disk, how did it guarantee the performance if it stores msg on disk instead of
Does the qstr struct in a kernel dentry hold the filename of a Linux file?
Below is a snippet of the Linux dentry struct from http://lxr.free-electrons.com/source/include/linux/dcache.h#L150. The struct contains a member struct qstr d_name – definition below. I would like to know if this is the name of the particular file that would correspond to this dentry at runtime. What confuses me is that proc/PID/maps uses struct dentry_operations -> d_name (another member of dentry) to
What are these unfamiliar lines in the C preprocessed file?
This is an output of the GNU cpp on a Hello World program in C. I am wondering what do these lines mean? # Number Header_File_Location [Numbers] Are these some kind of dependencies? If yes, then on what? Line numbers? Answer Those are line number directives, and tells the compiler what line and file the next part of the source
How to detect that a child process has crashed?
A child process can: Exit normally (by exiting using exit(0),exit(22), exit(23)) — This is obviously specific to my application Exit abnormally (code throws an exception, receives an unhandled signal, core dumps, etc…) I am doing a fork/exec from a parent process and looping on waitpid, when I detect that child process has exited I would like to determine the reason