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| <h4 class="subsection">27.6.1 Data Structures for the Shell</h4> |
| |
| <p>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. |
| |
| <p>The sample shell deals mainly with two data structures. The |
| <code>job</code> type contains information about a job, which is a |
| set of subprocesses linked together with pipes. The <code>process</code> type |
| holds information about a single subprocess. Here are the relevant |
| data structure declarations: |
| |
| <pre class="smallexample"> /* <span class="roman">A process is a single process.</span> */ |
| typedef struct process |
| { |
| struct process *next; /* <span class="roman">next process in pipeline</span> */ |
| char **argv; /* <span class="roman">for exec</span> */ |
| pid_t pid; /* <span class="roman">process ID</span> */ |
| char completed; /* <span class="roman">true if process has completed</span> */ |
| char stopped; /* <span class="roman">true if process has stopped</span> */ |
| int status; /* <span class="roman">reported status value</span> */ |
| } process; |
| |
| /* <span class="roman">A job is a pipeline of processes.</span> */ |
| typedef struct job |
| { |
| struct job *next; /* <span class="roman">next active job</span> */ |
| char *command; /* <span class="roman">command line, used for messages</span> */ |
| process *first_process; /* <span class="roman">list of processes in this job</span> */ |
| pid_t pgid; /* <span class="roman">process group ID</span> */ |
| char notified; /* <span class="roman">true if user told about stopped job</span> */ |
| struct termios tmodes; /* <span class="roman">saved terminal modes</span> */ |
| int stdin, stdout, stderr; /* <span class="roman">standard i/o channels</span> */ |
| } job; |
| |
| /* <span class="roman">The active jobs are linked into a list. This is its head.</span> */ |
| job *first_job = NULL; |
| </pre> |
| <p>Here are some utility functions that are used for operating on <code>job</code> |
| objects. |
| |
| <pre class="smallexample"> /* <span class="roman">Find the active job with the indicated </span><var>pgid</var><span class="roman">.</span> */ |
| job * |
| find_job (pid_t pgid) |
| { |
| job *j; |
| |
| for (j = first_job; j; j = j->next) |
| if (j->pgid == pgid) |
| return j; |
| return NULL; |
| } |
| |
| /* <span class="roman">Return true if all processes in the job have stopped or completed.</span> */ |
| 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; |
| } |
| |
| /* <span class="roman">Return true if all processes in the job have completed.</span> */ |
| int |
| job_is_completed (job *j) |
| { |
| process *p; |
| |
| for (p = j->first_process; p; p = p->next) |
| if (!p->completed) |
| return 0; |
| return 1; |
| } |
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