I have a really basic ncurses program to monitor machine statistics and launch remote xterms. It just sits on a window all day and helps me choose a not-heavily-loaded machine to work on. It works fine, and I love it dearly. But it's really fat. Much fatter than it needs to be, I think.
The program basically is as follows:
void * run(void * task) {
// once per minute:
popen( /* stats checking command */ )
// save output to global var
pclose
}
int main() {
// setup ncurses with halfdelay
for ( /* each machine */ )
pthread_create(somethread, NULL, run, (void *)somestruct);
while ( ( c = getch() ) != 'q' )
for ( /* each machine */ )
// print machine stats
// maybe launch an xterm
// die gracefully
}
And as stated above, it works just fine. The problem is that each thread has all the ncurses baloney tucked in private memory leading to one very fat process with a boatload of wasted bits.
The question, then, is this: how can I re-write or re-arrange this program so that each pthread doesn't carry around all the unnecessary ncurses stuff?
Side-question: You'll have to really sell me on it, but does anyone know of a better method than ncurses to do this? I want the stats on fixed positions in the terminal window, not scrolling text.
Related
Good day!
first time posting on stack overflow. Hope, I get this right.
For an exercise project, I would like my program to start vim or nano (doesn't matter for now) before proceeding.
Using the below code, vim starts. I.e. I can see the vim interface in the terminal window.
But: As soon as I start typing, after one or two characters, vim crashes giving me the following output:
Vim: Error reading input, exiting...
Vim: Finished.
Here's my code snippet:
pid_t childPid = fork();
if (childPid) {
// ...
}
else {
// open [filename.md] in vim
char * vim = "/bin/vim";
filePath = "/home/myusername/Documents/test.md";
execl(vim, vim, filePath, NULL);
}
Not sure, if I have to block the input recognition of the parent process or similar.
Guess I went a bit too far for my level of knowledge. It would be great to have a solution anyway. I think knowing a bit of how to solve this, might help when I encounter this topic later on.
I was able to fix this a little bit later. I had forgotten to make sure the parent process waits for the child process. After adding wait, everything worked as I expected.
Hi I am new to the linux environment. I am trying to create daemon process.
#include<stdio.h>
int main()
{
int a=10,b=10,c;
c=sum(a,b);
printf("%d",c);
return (0);
}
int sum(int a,int b)
{
return a+b;
}
I want to create daemon process of it. May i know how can do this? Any help would be appreciated. Thank you.
A daemon generally doesn't use its standard input and output streams, so it is unclear how your program could be run as a daemon. And a daemon program usually don't have any terminal, so it cannot use clrscr. Read also the tty demystified page, and also daemon(7).
I recommend reading some good introduction to Linux programming, like the old freely downloadable ALP (or something newer). We can't explain all of it here, and you need to read an entire book. See also intro(2) and syscalls(2).
I also recommend reading more about OSes, e.g. the freely available Operating Systems: Three Easy Pieces textbook.
You could use the daemon(3) function in your C program to run it as a daemon (but then, you are likely to not have any input and output). You may want to log messages using syslog(3).
You might consider job control facilities of your shell. You could run your program in the background (e.g. type myprog myarg & in your interactive shell). You could use the batch command. However neither background processes nor batch jobs are technically daemons.
Perhaps you want to code some ONC-RPC or JSONRPC or Web API server and client. You'll find libraries for that. See also pipe(7), socket(7)
(take several days or several weeks to read much more)
First find what are the properties of daemon process, as of my knowledge a daemon process have these properties:
Should not have any parent (it itself should be parent)
Process itself is a session leader.
Environment change to root.
File mode creating mask should be zero.
No controlling terminal.
All terminal should be removed
Should not be un-mounted .
Implement the code by considering above properties which is
int i=0;
int main()
{
int pid;
pid=fork();
if(pid!=0) {
/** you can add your task here , whatever you want to run in background **/
exit(0);
}
else
{
setsid();//setting sessions
chdir("/");//root.. should'nt beunmounted
umask(0);
close(0);//all terminal are removed
close(1);
close(2);
while(1)
{
printf("i = %d \n",i);
i++;
}
}
return 0;
}
or you can go through man page of daemon()
int daemon(int nochdir, int noclose);
I hope it helps.
Instead of writing the code to make the C program a daemon I would go with an already mature tool like supervisor:
http://supervisord.org/
I think this below will work
screen cmd arg1 arg2
You can also try
nohup cmd arg1
I'm trying to make a game in C using SDL_ttf to display the score every time the diplay is refreshed. The code looks like :
SDL_Surface *score = NULL;
TTF_Font *font;
SDL_Color color = { 255, 255, 255 };
font = TTF_OpenFont( "/home/sophie/Bureau/snake/data/ubuntu.ttf", 28 );
if (font == NULL) {
printf("%s\n", TTF_GetError());
}
score = TTF_RenderText_Solid( font, "score to display", color );
SDL_BlitSurface( score, NULL, screen, NULL );
SDL_Flip(screen);
When I launch the game, everything works properly, but after a while the game crashes and I get the following error :
Couldn't open /home/sophie/Bureau/snake/data/ubuntu.ttf
libgcc_s.so.1 must be installed for pthread_cancel to work
Abandon (core dumped)
I tried different fonts but I still have this problem.
Then I used a counter in the main loop of the game and found that the game always crashes after the 1008th time, regardless of the speed I wanted it to work at (in snake everything goes faster when you score points).
I don't know where does the problem comes from, nor what exactly does the error message mean.
Please tell me if you have any ideas, or if my question is poorly formulated. I looked on several forums and found nothing corresponding to my case, I could use any help now !
Thanks in advance
It looks like you're repeatedly opening the font every time you go through this function:
font = TTF_OpenFont( "/home/sophie/Bureau/snake/data/ubuntu.ttf", 28 );
While it may not be in the main game loop as Jongware suspected, you mentioned that after 1008 executions through this code path, the code crashes.
What is happening is that some resource is being leaked. Either the resource needs to be released by calling TTF_CloseFont() or (more efficient) hold onto the handle after the first time you open it and re-use it each time. Use a static declaration for the font and initialize to NULL:
static TTF_Font *font = NULL;
Then, if it hasn't been opened yet, open it:
if (!font) {
font = TTF_OpenFont( "/home/sophie/Bureau/snake/data/ubuntu.ttf", 28 );
}
This will initialize font the first time while subsequent iterations over the code will not unnecessarily re-do the process and leak the resource.
You mentioned that the code crashes after 1008 times through this function. That's pretty close to 1024. As memory serves, Linux has a limit of 1024 file handles per process (this is probably tunable in the kernel but I have run into this limitation in debugging resource leaks before). There are probably 16 other file handles open by your process and then 1 process being leaked by each invocation of TTF_OpenFont. Once you go above 1024, boom.
You can check the number of open file handles of a particular process (<pid>) by inspecting the number of file descriptors in /proc/<pid>/fd/.
Linux C program:
What function call can check if running in X Window?
If not in X Window, then printf.
Do you mean something like this:
#include <X11/Xlib.h>
// ...
char *display_name = NULL;
/* connect to X server */
if ( (display=XOpenDisplay(display_name)) == NULL )
{
//printf or whatever
}
What do you mean "running in X Window"? Do you mean whether your app is running inside a terminal emulator, like rxvt or xterm instead of a physical console? If so you could use the TERM variable I guess, but it's not reliable (since the user can change it to whatever).
The more important quesion is why is this information important to your application?
I wrote a C program/LaunchDaemon that checks if my MacBook is at home (connected to my WLAN). If so, it disables my password protection; if not, it enables it.
Easy. But the problem is that when I take my MacBook anywhere else and password protection is disabled, it will wake up without a password protection.
My fix for this would be: enable the password protection every time just before it goes to sleep.
QUESTION: is there any way find out when my Mac is preparing for sleep? Some interupt I can let my program listen to?
You can do it using I/O Kit, check Apple's QA1340: Registering and
unregistering for sleep and wake notifications. You may also want to
analyze the SleepWatcher utility sources or use/integrate for your needs.
From the homepage:
SleepWatcher 2.2 (running with Mac OS X 10.5 to 10.8, source code included)
is a command line tool (daemon) for Mac OS X that monitors sleep, wakeup and
idleness of a Mac. It can be used to execute a Unix command when the Mac or
the display of the Mac goes to sleep mode or wakes up, after a given time
without user interaction or when the user resumes activity after a break or
when the power supply of a Mac notebook is attached or detached. It also can
send the Mac to sleep mode or retrieve the time since last user activity. A
little bit knowledge of the Unix command line is required to benefit from
this software.
I attach below the contents of my C file beforesleep.c which executes some command line commands (in my case shell commands and AppleScript scripts) when a "will sleep" notification is received.
Where you can put your code:
In order to run your code when the mac is going to sleep, just replace the system(...) calls with the code you wish to run.
In my case, I use system() as it allows me to run shell commands passed as strings, but if you prefer to run just C code instead, you can just put your C code there.
How to build it
In order to build this file, I run:
gcc -framework IOKit -framework Cocoa beforesleep.c
Remark
If you are going to use this code, make sure it is always running in background. For example, I have a Cron job which makes sure that this code is always running, and it launches it again in case it is accidentally killed for any reason (although it never happened to me so far). If you are experienced enough, you can find smarter ways to ensure this.
Further info
See this link (already suggested by sidyll) for more details about how this works.
Code template
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <mach/mach_port.h>
#include <mach/mach_interface.h>
#include <mach/mach_init.h>
#include <IOKit/pwr_mgt/IOPMLib.h>
#include <IOKit/IOMessage.h>
io_connect_t root_port; // a reference to the Root Power Domain IOService
void
MySleepCallBack( void * refCon, io_service_t service, natural_t messageType, void * messageArgument )
{
switch ( messageType )
{
case kIOMessageCanSystemSleep:
IOAllowPowerChange( root_port, (long)messageArgument );
break;
case kIOMessageSystemWillSleep:
system("/Users/andrea/bin/mylogger.sh");
system("osascript /Users/andrea/bin/pause_clockwork.scpt");
IOAllowPowerChange( root_port, (long)messageArgument );
break;
case kIOMessageSystemWillPowerOn:
//System has started the wake up process...
break;
case kIOMessageSystemHasPoweredOn:
//System has finished waking up...
break;
default:
break;
}
}
int main( int argc, char **argv )
{
// notification port allocated by IORegisterForSystemPower
IONotificationPortRef notifyPortRef;
// notifier object, used to deregister later
io_object_t notifierObject;
// this parameter is passed to the callback
void* refCon;
// register to receive system sleep notifications
root_port = IORegisterForSystemPower( refCon, ¬ifyPortRef, MySleepCallBack, ¬ifierObject );
if ( root_port == 0 )
{
printf("IORegisterForSystemPower failed\n");
return 1;
}
// add the notification port to the application runloop
CFRunLoopAddSource( CFRunLoopGetCurrent(),
IONotificationPortGetRunLoopSource(notifyPortRef), kCFRunLoopCommonModes );
/* Start the run loop to receive sleep notifications. Don't call CFRunLoopRun if this code
is running on the main thread of a Cocoa or Carbon application. Cocoa and Carbon
manage the main thread's run loop for you as part of their event handling
mechanisms.
*/
CFRunLoopRun();
//Not reached, CFRunLoopRun doesn't return in this case.
return (0);
}