How can I split processes using C?
For example, in bash, I can use the command:
screen
You need to use fork() function.
The only way in C to create a new child process is the system call fork. All new process on UNIX/Linux are created with fork.
The child process is a copy of the parent process, the return value of fork call indicate if the current process is the parent (>0 : PID of the child process) or the child (0) or if the child process cannot be created (-1).
Related
I'm looking for a way to read from STDIN(console) in child process, after closing parent process.
My program should be like:
parent process forks and creates child process.
After creating child process, parent MUST be closed. I can not use functions such as wait() etc.
The thing is, when I exit from parent process, I can not read from console anymore. Is there any way to 'pass the control' to child process, instead of passing it back to shell ?
Instructions:
Process 1: reads data (sigle lines) from standard input stream and passes it with ipc message queue to process 2.
Process 2: receives data send by process 1 and prints it in standard output stream.
Two processes should be executed automatically from 1 initiative process. After executing child processes, initiative process should immediatelly close.
If in a simple C program I am writing 4 calls to the fork() API and when I execute this program then the total processes created will be 16 on Linux.
Using getpid() can get the process id of that current process.
Using getppid() can get the parent process id of the calling process.
Question: How can the last child know the process id of the first process
(the ancestor's parent id) from which I call the fork() API four times?
NOTE: The assumption is that all processes are running; nobody died.
Just use
first = getpid()
before all the forks, and use that variable in the children.
1) You can use process tree command called ps l (for ppid seperate table is there.)
2) Using getppid() you can check recursively and reach to main process. Here you need some smart logic for this.
I am creating a parent process that creates a child using fork(), and then creates a shared memory block that can be accessed by both the parent and the child. I have created child processes using the WIN32 api (by creating several .exe files and running them all and then calling them using the createProcess() function), but am a bit unsure of the steps for linux.
I have created a separate C file that contains the child's code. I assume I will create the child process using fork, then while in the child process (pid == 0) use an exec() command to call the other C file? Do I need to first run the other file? Or can it just be sitting in the same directory?
Any help is appreciated
Thanks
After fork (), there are two processes, the parent and the child. The fork system call in the parent process returns the process id of the child. In the child process, fork () returns 0. So, if the return value of fork () is zero, you can call an exec system call with the executable file name of the program for the child process.
i have a c problem can any one help me . i wrote a code of process creation in c language , it uses pid & fork() call. the fork call is use for making child process now can any body tell me how to make parent process? i know that creating a child in process make the process parent automatically but i want to make a parent process right from the start so can any one tell me how to do this,
Secondly i just create the process i don't know how to use it i cant assign any work(computation) to it.so can any one tell me how to use the process for work?
Third one i want to give a name to my process how can i do it & how i can control their execution?
please if anyone can enlighten me than please help me to understand all this.
i shall be thank full for this forever
thanks in advance
The fork call creates a new process that is identical to the existing process except for a few minor differences such as its pid, parent pid. The original process carries on from exactly the same place and this is the parent process. Which means your question is basically meaningless. You don't create the parent process, the original process becomes the parent process once it creates a child process.
It's a bit like asking "I created a child by getting pregnant and giving birth, but how do I create the parents?" You are a parent automatically.
Back to computers...
When you fork, the system call returns the pid of the child to the parent and 0 to the child, so you should have code something like:
int pid = fork();
if (pid == 0)
{
// in child, do child processing - normally exec an executable
}
else if (pid > 0)
{
// in parent, do some processing - often wait for child to complete
}
else
{
// fork failed - handle the error
}
When you fork a process, one process becomes two processes. Each continues running at exactly the same place. The only difference is that the fork returns the PID of the child process to the parent process and returns the value 0 to the child process.
Without any help, the child process does not know its parent. If the two processes need to communicate with one another then they will need to use some sort of IPC mechanism.
A common form of IPC is pipe. If one opens pipes before forking, then both the child and the parent keep the open file descriptors. This will allow both processes to communicate with one another. The parent is now free to communicate its PID to the child process if so desired.
Secondly i just create the process i don't know how to use it i cant assign any
work(computation) to it
You need to use fork and exec in pair make it run the program you want to execute.
Here is the wiki link for more information.
Fork-exec is a commonly used technique in Unix whereby an executing process spawns a new program. fork() is the name of the system call that the parent process uses to "divide" itself ("fork") into two identical processes. After calling fork(), the created child process is actually an exact copy of the parent - which would probably be of limited use - so it replaces itself with another process using the system call exec().
To create a parent process, take your code for creating a child and reverse the roles of parent and child. Presto change-o, the new process is the parent and the old process is the child.
For communications between the processes, use a pipe(2), or several. Also, there is shared memory.
To control execution, use kill(2) and wait(2). I'm not sure about assigning names, we might need to know what platform you're on.
About renaming (I assume you mean the name displayed by ps), to "rename" a process, just copy your new name into argv[0]
If not, how can we start a background process in C?
In Unix, exec() is only part of the story.
exec() is used to start a new binary within the current process. That means that the binary that is currently running in the current process will no longer be running.
So, before you call exec(), you want to call fork() to create a new process so your current binary can continue running.
Normally, to have the current binary wait for the new process to exit, you call one of the wait*() family. That function will put the current process to sleep until the process you are waiting is done.
So in order to create a "background" process, your current process should just skip the call to wait.
Use the fork() call to create a new process, then exec() to load a program into that process. See the man pages (man 2 fork, man 2 exec) for more information, too.
Fork returns the PID of the child, so the common idiom is:
if(fork() == 0)
// I'm the child
exec(...)