ash: converge waiting code to dash in its form, add comments, no code changes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 30 insertions, 26 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 14c59a769..ad1b9fd9f 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -4412,11 +4412,12 @@ sprint_status48(char *os, int status, int sigonly)
         return s - os;
 }
 
-#define DOWAIT_NONBLOCK 0
-#define DOWAIT_BLOCK    1
-#define DOWAIT_BLOCK_OR_SIG 2
+/* Inside dowait(): */
+#define DOWAIT_NONBLOCK 0       /* waitpid() will use WNOHANG and won't wait for signals */
+#define DOWAIT_BLOCK    1       /* waitpid() will NOT use WNOHANG */
+#define DOWAIT_CHILD_OR_SIG 2   /* waitpid() will use WNOHANG and if got 0, will wait for signals, then loop back */
 #if BASH_WAIT_N
-# define DOWAIT_JOBSTATUS 0x10   /* OR this to get job's exitstatus instead of pid */
+# define DOWAIT_JOBSTATUS 0x10  /* OR this to get job's exitstatus instead of pid */
 #endif
 
 static int
@@ -4437,9 +4438,16 @@ waitproc(int block, int *status)
                         err = waitpid(-1, status, flags);
                 while (err < 0 && errno == EINTR);
 
+                /* Return if error (for example, ECHILD); or if pid found;
+                 * or if "block" is DOWAIT_NONBLOCK (=0), in this case return -1.
+                 */
                 if (err || (err = -!block))
                         break;
 
+                /* "block" is DOWAIT_CHILD_OR_SIG. All children are running
+                 * (waitpid(WNOHAG) above returned 0), wait for signals:
+                 */
+
                 //simpler, but unsafe: a signal can set pending_sig after check, but before pause():
                 //while (!gotsigchld && !pending_sig)
                 //      pause();
@@ -4451,12 +4459,12 @@ waitproc(int block, int *status)
 
                 sigclearmask();
         } while (gotsigchld);
+        /* If we fall off the loop, err is 0, which means we got a !SIGCHLD signal */
 
         return err;
 }
 
-static int
-waitone(int block, struct job *job)
+static int waitone(int block, struct job *job)
 {
         int pid;
         int status;
@@ -4495,32 +4503,30 @@ waitone(int block, struct job *job)
 
         for (jp = curjob; jp; jp = jp->prev_job) {
                 int jobstate;
-                struct procstat *ps;
-                struct procstat *psend;
+                struct procstat *sp;
+                struct procstat *spend;
                 if (jp->state == JOBDONE)
                         continue;
                 jobstate = JOBDONE;
-                ps = jp->ps;
-                psend = ps + jp->nprocs;
+                spend = jp->ps + jp->nprocs;
+                sp = jp->ps;
                 do {
-                        if (ps->ps_pid == pid) {
-                                TRACE(("Job %d: changing status of proc %d "
-                                        "from 0x%x to 0x%x\n",
-                                        jobno(jp), pid, ps->ps_status, status));
-                                ps->ps_status = status;
+                        if (sp->ps_pid == pid) {
+                                TRACE(("Job %d: changing status of proc %d from 0x%x to 0x%x\n", jobno(jp), pid, sp->ps_status, status));
+                                sp->ps_status = status;
                                 thisjob = jp;
                         }
-                        if (ps->ps_status == -1)
+                        if (sp->ps_status == -1)
                                 jobstate = JOBRUNNING;
 #if JOBS
                         if (jobstate == JOBRUNNING)
                                 continue;
-                        if (WIFSTOPPED(ps->ps_status)) {
-                                jp->stopstatus = ps->ps_status;
+                        if (WIFSTOPPED(sp->ps_status)) {
+                                jp->stopstatus = sp->ps_status;
                                 jobstate = JOBSTOPPED;
                         }
 #endif
-                } while (++ps < psend);
+                } while (++sp < spend);
                 if (!thisjob)
                         continue;
 
@@ -4532,8 +4538,7 @@ waitone(int block, struct job *job)
                          */
                         thisjob->changed = 1;
                         if (thisjob->state != jobstate) {
-                                TRACE(("Job %d: changing state from %d to %d\n",
-                                        jobno(thisjob), thisjob->state, jobstate));
+                                TRACE(("Job %d: changing state from %d to %d\n", jobno(thisjob), thisjob->state, jobstate));
                                 thisjob->state = jobstate;
 #if JOBS
                                 if (jobstate == JOBSTOPPED)
@@ -4568,8 +4573,7 @@ waitone(int block, struct job *job)
         return pid;
 }
 
-static int
-dowait(int block, struct job *jp)
+static int dowait(int block, struct job *jp)
 {
         smallint gotchld = *(volatile smallint *)&gotsigchld;
         int rpid;
@@ -4795,9 +4799,9 @@ waitcmd(int argc UNUSED_PARAM, char **argv)
          * the trap is executed."
          */
 #if BASH_WAIT_N
-                        status = dowait(DOWAIT_BLOCK_OR_SIG | DOWAIT_JOBSTATUS, NULL);
+                        status = dowait(DOWAIT_CHILD_OR_SIG | DOWAIT_JOBSTATUS, NULL);
 #else
-                        dowait(DOWAIT_BLOCK_OR_SIG, NULL);
+                        dowait(DOWAIT_CHILD_OR_SIG, NULL);
 #endif
                         /* if child sends us a signal *and immediately exits*,
                          * dowait() returns pid > 0. Check this case,
@@ -4838,7 +4842,7 @@ waitcmd(int argc UNUSED_PARAM, char **argv)
                         job = getjob(*argv, 0);
                 }
                 /* loop until process terminated or stopped */
-                dowait(DOWAIT_BLOCK_OR_SIG, job);
+                dowait(DOWAIT_CHILD_OR_SIG, job);
                 if (pending_sig)
                         goto sigout;
                 job->waited = 1;