Process Operations

Abstract

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• Operation is described in C

Process Creation

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• A 2 steps process - fork(), exec()
• The two-step process gives the child the flexibility to manipulate its file descriptors(STDIN in the above example) after the fork but before the execve in order to accomplish redirection of standard input, standard output, and standard error
• The code below creates a child Process (进程), Pipe (管道) the input of the child process, load and execute child process

int pid = fork();
if (pid == 0)
{
	dup2(pipe_fds[numProcesses - 2][READ_STREAM], STDIN_FILENO);
	closePipes(numProcesses, pipe_fds);
	execvp(sub_process[0], (char *const *)sub_process);
}

Process Termination

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2 Voluntary Ways

1. Process (进程) ends its job
2. Process (进程) hits an error during execution and exits gracefully

2 Involuntary Ways

1. Fatal error - which couldn’t be handled by the Process (进程) itself (eg. Memory Failure)
2. Termination by other process (killem all!)

POSIX

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fork()

• Creates an exact duplicate of the original Process (进程)
• When return value is 0: we are inside the duplicate process
• Duplicated process’ s Process IDentifier (PID) in parent process