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Unix Processes Unix Fork System Call Unix Fork System Call Unix Fork

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Unix Processes Unix Fork System Call Unix Fork System Call Unix Fork CIS 415 Unix Processes ß PID (process ID) - unique number used to identify each process Unix Process Management ß Process creation system calls fork exec ß Process destruction system call kill 2 Unix fork system call Unix fork system call ß Parent process (creator, old process) ß BEFORE fork ß Child process (created, new process) Printf(“one\n”); ß After fork, two processes exist and are running concurrently. Pid = fork(); Printf(“two\n”); ß fork causes a new process to be created with Process A a duplicate of the parent’s code ß AFTER fork ß fork returns a value of 0 to the child. Printf(“one\n”); Printf(“one\n”); ß fork returns the child’s PID to the parent Pid = fork(); Pid = fork(); ß (greater than 0) Printf(“two\n”); Printf(“two\n”); 3 4 Parent process A Child process B Unix fork system call Unix exec system call /* spawn new process using fork */ ß Replaces old process with new code. main() { ß After exec, the process is running a new pid_t pid; piece of code. printf(“Just one process so far\n”); printf(“Calling fork\n”); ß Process ID is the same. pid = fork(); /* create new process */ ß exec never returns except if error. if (pid == 0) ß exec provides a means for passing printf(“I am the child\n”); parameters from the old to the new. else if (pid > 0) printf(“I am the parent; my child has pid %d\n”, ß Family of exec system calls differ in where pid); the code comes from and how parameters are else passed. printf(“fork returned error code, no child\n”); } 5 6 Interrupts 1 CIS 415 Unix exec system call Unix process creation •int main( void ) { ß BEFORE exec • • pid_t pid; /* type is from sys/types.h */ Printf(“hello\n”); • int error_code; • pid = fork(); Pid = execl(“bin/ls”); Printf(“never\n”); • if( pid == 0 ) { This code never executed. • printf( "\nI am the child, running %s.\n" • , program_name ); Process A • ß AFTER exec • /* never returns if all goes well */ Code for ls • error_code • = execl(“/bin/program_name”, • , “program_name”, • , "-l", (char*)0 ); • printf( "Error running ls, execl returned %d.",error_code ); Process B (Note that Process A no longer exists.)7 • exit(0); 8 • } • Unix process creation (cont) Unix process id system calls •else { • printf( "\nI am the parent process.\n"); • getpid - returns the pid of this process • printf("My child is pid:%d\n", (long)pid ); • getppid - returns pid of this process’ parent • exit(0); • } •} • 9 10 Unix process monitoring Unix process monitoring The Unix ps command (process status) The Unix time command (process execution stats) time <process binary file> Allows user to query status of processes. Unix will display information such as: Unix will display the following timing information: process ID, parent process ID user system elapsed % priority, memory mgmt info, runtime Where user is CPU time in user code system is CPU time in kernel code elapsed is total time in system % is percentage of elapsed time that is CPU time 11 12 Interrupts 2.
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