Is there a way to pass data (ex: int value) from one process to another process in c?
In my experience, we just can send signal from one process to another. But looks like there is no way to "attach" some information along with that signal to another process.
With the sigqueue function, you can pass a single integer or pointer along with a signal (but keep in mind, pointers will be useless if the target of the signal is another process, since different processes don't share address space).
Some other methods are pipes, shared memory (POSIX or SysV style), files, ...
You can use one of the various Inter Process Communication Mechanisms available.
Use Google. As a reference you can also look here
A clean, portable, powerful way is use Socket.
You can use pipes to do that. The main purpose of pipes is to communicate data between different processes.
Pipes are the simplest mechanism offered by the operating system for inter-process communication. A pipe is a communication buffer between two processes: it has two descriptors, one for writing another for reading. Write and read operations are done in a FIFO order (first-in-first-out).
There are two kinds of pipes: unnamed pipes and named pipes (also known as FIFOs).
Unnamed pipes only allow communication between hierarchically related processes (parent and child processes);
Named pipes allow the communication between any process. A special file is created in the file-system through
If you want some example code just go here: http://pastebin.com/1W216nyN
I think we can use global variable between process, not sure but. If any one tried then please let me know. If we use a header which contain extern valriable , we can use this in another main() which is nothing but a independednt program (process). but we have to link the two main() together which executing.
Related
I'm using C and Winsock2 for my learning project.
I have some questions that I hope some one can confirm.
Let say I have 2 unrelated processes, process A and process B ( without using CreateProcess ). By unrelated I mean it's not parent and child.
1)
Is it possible in Windows to Accept a socket in process A and pass it to process B if they are unrelated?
2)
I guess i have to use WSADuplicateSocket? but that only works for related processes?
I hope someone can explain and confirm the above..
Is it possible in Windows to Accept a socket in process A and pass it to process B if they are unrelated?
Yes, via WSADuplicateSocket():
The WSADuplicateSocket function is used to enable socket sharing between processes. A source process calls WSADuplicateSocket to obtain a special WSAPROTOCOL_INFO structure. It uses some interprocess communications (IPC) mechanism to pass the contents of this structure to a target process, which in turn uses it in a call to WSASocket to obtain a descriptor for the duplicated socket. The special WSAPROTOCOL_INFO structure can only be used once by the target process.
I guess i have to use WSADuplicateSocket?
Yes.
but that only works for related processes?
No. It will work fine between any 2 processes, as long as process A knows process B's Process ID, as that is a required parameter of WSADuplicateSocket().
Can you use a pipe to share threads between two processes in C? I am writing my own shell and want to know if this implementation would be more optimal, if it is even possible?
Each thread is specific to a process and share memory of the calling thread.
If you want efficient inter process communication, you can use shared memory.
See http://man7.org/linux/man-pages/man7/shm_overview.7.html
So I want to pass a variable from one c program to another c program.
For example:
main()
{
char str[]="Hello,there!";
system("program2.exe");
}
And I want to use str[] in program2.exe. Is there a way to pass a variable to another program?
I used files to write data from first program and read data from second program but I want to know is there any other way to do this?
Is it good to use files for passing data from program to another?
You can't literally pass a variable between two processes because each process on a system will generally have it's own memory space - each variable belongs to a process and therefore can't be accessed from another process (or so I believe). But you can pass data between processes using pipes.
Pipes are buffers that are implemented by the OS and are a much more effective method of sharing data between processes than files (yes, you can use files for inter-process communication). This is because files must be written to a disk before being accessed which makes them slow for inter-process communication. You'd also have to implement some kind of method for ensuring the two processes don't corrupt a file when reading and writing to it.
Also, pipes can be used to ensure continuous communication between two processes, making them useful in many situations. When using half duplex pipes (linked above), you can have a pipe for each process to establish a communication channel between them (i.e. a one way communication channel for each).
you can:
1) pass arguments to a program.
2) use sockets to communicate between processes.
Linux Kernel version 3.2 and further have a capability called cross memory attach.
Here is the link to it. I was not able to get a lot of help in that regard.
http://man7.org/linux/man-pages/man2/process_vm_readv.2.html
In the syntax we need the address of the remote memory where we want to write to or read from. My question is how do I get the address of this remote memory if I am using fork().
Suppose I am sending something from parent process to child process using cross memory attach. How do I send the address of the remote memory to the parent process from the child process?
The system calls process_vm_readv and process_vm_writev are meant for fast data transfer between processes. They are supposed to be used in addition to some traditional way of interprocess communication.
For example, you may use a regular pipe or fifo to transfer the required addresses between your processes. Then you may use those addresses to establish faster process_vm_ communication. The simpliest way to transfer something between forked processes should be the pipe() function (man 2 pipe has a good example of its usage). There are many other ways to do so of course, like using sockets or messages. You can even write an address to a file and let the other process read it.
let's say I have 2 processes and I have a variable I want to pass from the first one to the second one. I know I can declare a global variable and pass it by reference among differents functions, but I don't know if it is possible to pass a variable among different processes.
I heard that each process is assigned its own portion of virtual memory and that one process cannot access another process' memory space. Is it that true? Or is is actually possible for two processes to share a variable and therefore mutex mechanisms are needed?
I don't know if it is possible to pass a variable among different processes.
No, it is not possible, at least not in the classical sense of passing a variable. You have many options, though: inter-process communication can be done through shared memory (sometimes implemented through memory-mapped files), named pipes, etc.
Or is is actually possible for two processes to share a variable and therefore mutex mechanisms are needed?
Yes, you should look up shared memory, or more generally, IPC / interprocess communication.
If the second process is started from the first one, you could pass it as command line parameter.
Otherwise you should rely on some inter-process communication method (like Socket or FIFO, also known as named pipe).
You could have a look to this other post:
Interprocess Communication via file