Programming :: Creating Multiple Processes Using Fork
Oct 23, 2010
As an assignment i was doing a program to create two process using fork and pass messages between them using message queue.Did it worked well until my friend tried to copy it using scp.suddenly all hell broke loose as processes without ran syncronisation ie. in tech terms the process just wont wait wen a message queue is empty.it keeps on executing randomly.but after a reboot .. everything worked fine. until again i tried to do scp on my system on purpose. and again the program just went mad.
the wrong part of the forum but basically im working on a project and getting no where what so ever and i was wondering if i could get your help. Basically i have to create two scripts do:
The parent script which is going to: o spawn several child processes. o keep track of the progress of the child processes.
I'm looking for a way in Perl to be able to take a list of servers, ssh multiple commands to it and store the results. If I do this process serially, sometimes one server will hang the whole script and if it doesn't, it still takes hours to complete.
I'm thinking what I need to do is make a parent loop that calls out a separate process that passes the server name to the child sub process and then executes all the commands I have defined in its own process. If one server 'hangs', at least that won't stop the script from doing all the other servers in the list.
I'm guessing using the fork() command would serve me best, however, all the online descriptions I have found have been vague at best.
Suppose I have a server, foo, that runs on port 5555. I can make one connection to it at a time on that port. I want xinetd to fork new instances of foo so multiple clients can connect to it.
Here's a configuration entry:
1) How does xinetd fork a new instance of foo when a previous instance is already listening on port 5555? Wouldn't the new process fail to launch because port 5555 is already in use by the previous process?
2) Suppose five clients connect simultaneously, and xinetd forks five instances of foo. When the clients disconnect, does xinetd leave all five instances running?
As part of my ongoing project I need to put together a messaging server of sorts. So far I have coded a server which accepts multiple connections, which then runs a function that will perform a task, see below.On this sever I have a global structure which is populated using the data found in a read() buffer. However with each fork() that runs the below function each process is handed a blank structure. How could I go about allowing each fork() child process access the same structure?
My code should hopefully show what I am trying to do? Code: void listen_for_client(int sock) {
Now,I created one parent and two children. I must create some value as random in child1 and child1 has to send these values to child2.Child2 must read them.. now,I cant create some random values and i can send them.But child2 doesnt work. I have two functions. One them is writing, another one is reading. Child2 uses reading function,but it doesnt work (child2 cant call it, because writing function in endless loop) What i must do? I used wait,usleep... No way.. I attached my file and also there is code..
Just coming over from Windows here... where I've been using "CreateProcess" which returns a value depending on whether the process was created successfully or not.
Now I'm trying to create a process on linux and I've been learning about fork/exec, and I've been struggling with the fact that there seems to be no easy way to know (within the original parent process) if exec succeeded or not. (without forcing the parent process to hang around polling it or something).
Anyway, I've now just discovered the posix_spawn function, and it seems exactly what I need. However I'm finding the documentation a little hard to understand. In particular, I can't find actual confirmation that it will definitely return an error if creating the process fails (like CreateProcess does on windows). So can anyone confirm that for me?
The text on the documentation states: "If posix_spawn() or posix_spawnp() fail for any of the reasons that would cause fork() or one of the exec family of functions to fail, an error value shall be returned as described by fork() and exec"
This makes me think it uses exec/fork under the hood, and so I wonder if it can be trusted..?
And also, most of the examples on the internet for creating processes use fork/exec, so I wonder if there is some catch with posix_spawn I haven't read about... (since it seems a much simpler way of doing things)
I have been struggling with this for about a week now. I'm working with QuickUSB to send video streams to and from a device. I get the fastest results by fork()ing and exec()ing new processes everytime I run a pipeline, which works great when reading from files, but now i have to transition it so that i am reading/writing data over a QuickUSB bus. I have it working for each individual process, but i can't run multiple processes because it won't let me open the device. After looking through QuickUSB's API a little closer, i found that the QHANDLE type that they use to describe the usb device is actually just a usb_dev_handle *. From what i have found, this is an incomplete structure, so i am having trouble with opening it in the main process and passing it to each new process to write to it. I already have semaphores set up to prevent multiple processes using it at the same time. I just CANT find out how to utilize the same usb device between two process that are forked and exec. i also must do the exec() because otherwise my gtk and gstreamer fails for trying to share resources.
I have been doing programming since the last 5 years. however, i have used to cut and paste the template without knowing in depth since i am chasing the time to finish a certain project. The title above seems easy if we read the manual, its just that im kinda confuse just for a second. Hope you guys can help me to give a better understanding for me so that i can upgrade my knowledge.Well, during my normal practice cut and paste, i try to understand this code below :-
Code: pid_t pid; pid=fork(); if (pid < 0) {perror("Erro spawning process : "); exit(EXIT_FAILURE);}
i got basic knowledge about creating a single child from a parent using fork(). But when it comes into creating multiple children, i am simply stuck. I am trying to create two processes from a parent and it would wait for both two processes to finish. my attempt is as below
I have running license server on my server. Right now I would like to write small status script and check if software is running.My software include 3 deamons:
1) daemonA 2) daemonB 3) daemonC
My script should check, if each of this deamon is running. If all deamons are running then script should print short output: "License server is running" if one of this daemons is not running, output should "License server is not running". Is it possible to write small loop to check it ? Let say, loop will take new daemon name from deamons pool and will check if its running. Sometimes I need to check more than three daemons of one Program and I dont know how to write good script for this. Maybe somebody could help me with this loop that in the future I could also use; daemonD, daemonE, daemonF.etc.etc. if all daemons from pool is running then..."Software is running"
I know that fork() copies the address space of the calling process. Say, however, i have a linked list allocated. Will the list be copied over to the child process's space? If so, i would have to free them in the child process as well as the parent process, correct? Or will the variables be copied but not be pointing to any valid address? Or would it just kind of not do anything?example:
Q 1. The value of the variable pid returned by the fork() function will be greater than 0 in the parent process and equal to zero in the child process? but during forking, there values are exactly copied so what's went wrong here?
Q 2. "changes to the variable in one process is not reflected in the other process" why it is so? >> Even if we have variable i declared as a pointer or a global it wont make a difference.
Code:
int main() { int i, pid; i=10; printf("before fork i is %d
[code]....
Q. Through this program it is clear that both process is using the data from the same location, so where's the original value is residing when the child process is in execution.?
I'm trying to write a program that will fork a series of FTP sessions. For each session, there should be separate input and output files associated with stdin and stdout/stderr. I keep reading how I should be able to do that with dup2() in the child process before the execl(), but it's not working for me. Could someone please explain what I've done wrong? The program also has a 30-second sniper alarm for testing and killing of FTPs that go dormant for too long.
The code: (ftpmon.c) #include <stdio.h> #include <stdlib.h> #include <string.h>
[code]....
The output:
$ ftpmon Connected to gila-crstest.gilacorp.com (172.16.20.8). 220 (vsFTPd 2.0.1) ftp> waitpid(): Interrupted system call
Why am I getting the ftp> prompt? If the dup2() works, shouldn't it be taking input from my script and not my terminal? In stead, it does nothing, and winds up getting killed after 30 seconds. The log file is created, but it's empty after the run.
I have a monitoring program ( GIT link to sourceforge ) which I'm trying to use to track when a child exits/dies/whatever. I'm calling fork(), then close for 0,1,2, and then opening /dev/null, monitored.stdout, and monitored.stderr as a replacement. I'm not sure if I've done something incorrect (perhaps I should use dup2 for explicit assignment?) but it appears that printf() messages are just being blackholed. I've tried setting the line buffering as a last ditch effort. On a different system, using code similar to the spawn_monitor() function, this appears to work fine, which makes me think I'm relying on some implementation specific detail.
Relevant function, for those who don't click links:
This is the second new install of 10.4 on the same machine with the same issue. After boot, as soon as user logs into the desktop, sys mon shows cpu at 100 percent and a steady climb in ram usage. several processes are spawned continuously until all ram is consumed and then moves on to use scratch space.
Using top, the process count moves into over a thousand total processes. Some investigation using top, ps, and digging into the /proc folder shows a ppid of 1 If the machine is booted to shell, top shows 120 processes and is stable. Some of the processes running repetitively are the gnome toolbar, nautilus, and I wish I was clear headed enough to write the others down before I left work. I can certainly get a more complete list in the morning.
I have swapped out ram, and the processor with no success. I have also tried apt-get purge ubuntu-desktop then installing with apt, this did not resolve it. As mentioned at the top of the post, this is the second install with these symptoms. The first install started showing the issue about 10 hours after first boot. On this second install, all was working fine for a couple days before this started in.
when I start my application it creates a message queue and forks a process. The child process reads multicast packets from the network and writes to message queue. The parent process reads packets from message queue and compares source ip and sequence number (it is part of payload) with last 64K packets received to see if it has received a duplicate packet. I am using message queue as a buffer because I do not want child process to drop any packets while it is comparing it with previously received packets. The message queue is large enough to contain 64K packets. To compare the old packets I am using array of structures as circular buffer. During a spike I may receive 100 - 120 packets per milli second.
When I run my application, the parent process keeps up with the child process, I can see that with "ipcs -q". After about 30 seconds it cannot keep up and the size of message queue keeps increasing until it is full. When I run "top" I can see that one CPU/core is hundred percent busy while other 7 cores are idle. It seems that both processes are running on same core and the child process gets interrupts everytime there is a packet on the net and starves the parent process.I am running RHEL 5. The system has 24GB memory and my application is the only application running on it. It is a HP G6 server.
Whenever I monitor my CPU's, it seems only the first is ever utilized, with the second always being at 0%.Does this mean it is not being used, or just not being reported as in use?Is there anything I could do to improve the situation if it is not being used as much as it could be?On Windows, I can assign processes to both cores, or either one. Is there a way to do something similar in Linux?
My server is really slow. When I did a top -c or ps aux, below shows up. Shouldn't there be only one? Shall I kill all those processes and leave only one?
my computer is often very slow, to the point of stalling. I tty'd in and when I ran ps -ef I noticed about 10 /usr/sbin/apache2 -k start I dont even want 1 apache running. Any suggestions why these are running, or how to stop it? Well, I can stop it with a sudo killall, but how can I make sure it doesnt happen again?
I've got this problem for a few weeks and I cannot figure out. I'm pulling my hair out. I have a server installed PHP, lighttpd and redis. Sometimes, I got the following messages in the error log of lighty: Code: 2010-09-24 13:57:33: (mod_fastcgi.c.3011) backend is overloaded; we'll disable it for 1 seconds and send the request to anoth er backend instead: reconnects: 0 load: 567 2010-09-24 13:57:33: (mod_fastcgi.c.3011) backend is overloaded; we'll disable it for 1 seconds and send the request to anoth er backend instead: reconnects: 0 load: 626 and:
I wrote a program that multiplies 2 matrices using multi-threads and another one using multiple processes and shared memory. Both in C.I need to find the total memory usage of these programs. I know of the top command, but when my matrices are relatively small they don't even show up on top because they complete so fast, how can I find the memory usage for these instances?Also, how can I find the total turnaround time of my programs
I need to create subdirectories in about 300 existing directories - the subdirectory will have the same name in all 300 existing directories. How do I do this using the mkdir command using a regular expression or globbing?
I have a TCL framewrok for my test cases automation. This is been working for last 1 year. But yesterday it exited with exception when a function was called. The exception was given as fork: not enough memory while executing "spawn bash"(procedure "runtrigger" line 36) invoked from within "runtrigger $fnAfter $sid_l $mapver" ("trigger" arm line 6) invoked from within
I have a doubt about signals in C programming. I have done this little program to explain it. It creates a child process with fork and, when the child ends, receives the SIGCHLD signal and wait for its termination.Ok, quite easy, BUT when I execute this code the SIGCHLD signal is received twice, first as an error (returns -1) and the second one to finish the child process.I don't understand the meaning of the first received signal. Why is it generated? Is the code wrong? (if you add the SIGINT and press Ctrl+C during the execution it also receives two signals instead of one)
I created a user and I want the particular user in multiple groups. How Should I and after creating the user,If I want to delete that user from a particular group.
I have some novice to intermediate programming skills from a past life. What I want to do is create a program and run it on two separate computers to just get them communicating together over the network on a basic level. I would like to do this in a language that doesn't limit me to a specific OS, this way I can have a linux and windows computer talking. However, I would prefer a language that can be useful down the road as well. My second inspiration, next to networking, is web design and web programming, which I hope to dig into as well eventually.
I'm not aiming to do anything overtly-complicated. One example that comes to mind would be a program that forwards any typed characters on one computer over the network and displays them on the other, and vice-versa. I guess the program would run over TCP/IP. However, it would be nice to learn how to do this in a language that not only works on multiple OSes, but also has the ability to allow me to program my own communication protocol, aside from TCP/IP, down the road. My intention with all this is to learn some network programming for fun.
