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(libc.info)Data Structures

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Data Structures for the Shell
-----------------------------

   All of the program examples included in this chapter are part of a
simple shell program.  This section presents data structures and
utility functions which are used throughout the example.

   The sample shell deals mainly with two data structures.  The `job'
type contains information about a job, which is a set of subprocesses
linked together with pipes.  The `process' type holds information about
a single subprocess.  Here are the relevant data structure declarations:

     /* A process is a single process.  */
     typedef struct process
     {
       struct process *next;       /* next process in pipeline */
       char **argv;                /* for exec */
       pid_t pid;                  /* process ID */
       char completed;             /* true if process has completed */
       char stopped;               /* true if process has stopped */
       int status;                 /* reported status value */
     } process;
     
     /* A job is a pipeline of processes.  */
     typedef struct job
     {
       struct job *next;           /* next active job */
       char *command;              /* command line, used for messages */
       process *first_process;     /* list of processes in this job */
       pid_t pgid;                 /* process group ID */
       char notified;              /* true if user told about stopped job */
       struct termios tmodes;      /* saved terminal modes */
       int stdin, stdout, stderr;  /* standard i/o channels */
     } job;
     
     /* The active jobs are linked into a list.  This is its head.   */
     job *first_job = NULL;

   Here are some utility functions that are used for operating on `job'
objects.

     /* Find the active job with the indicated PGID.  */
     job *
     find_job (pid_t pgid)
     {
       job *j;
     
       for (j = first_job; j; j = j->next)
         if (j->pgid == pgid)
           return j;
       return NULL;
     }
     
     /* Return true if all processes in the job have stopped or completed.  */
     int
     job_is_stopped (job *j)
     {
       process *p;
     
       for (p = j->first_process; p; p = p->next)
         if (!p->completed && !p->stopped)
           return 0;
       return 1;
     }
     
     /* Return true if all processes in the job have completed.  */
     int
     job_is_completed (job *j)
     {
       process *p;
     
       for (p = j->first_process; p; p = p->next)
         if (!p->completed)
           return 0;
       return 1;
     }