Clean up issues in Unix_handlecomm preventing clean process exit (#413)

When Medley closes a stream open to a process it uses a "unixcomm"
command (3) which should close() the communication channel open with
the process and give it a chance to handle that and exit cleanly
before using a SIGKILL on it.  We can't determine apriori whether the
process is going to cooperate, so we're stuck trying for up to 0.1s
(arbitrary choice!)  waiting for the process to exit, then it gets a
SIGKILL, and we wait up to 0.1s again to see that it really exited.

src/unixcomm.c

@@ -372,7 +372,7 @@ LispPTR Unix_handlecomm(LispPTR *args) {
 
   /* Get command */
   N_GETNUMBER(args[0], command, bad);
-  DBPRINT(("\nUnix_handlecomm: trying %d\n", command));
+  DBPRINT(("\nUnix_handlecomm: command %d\n", command));
 
   switch (command) {
     case 0: /* Fork pipe process */
@@ -435,6 +435,7 @@ LispPTR Unix_handlecomm(LispPTR *args) {
         UJ[PipeFD].PID = (d[1] << 8) | d[2] | (d[4] << 16) | (d[5] << 24);
         close(sockFD);
         unlink(PipeName);
+        DBPRINT(("New process: slot/PipeFD %d PID %d\n", PipeFD, UJ[PipeFD].PID));
         return (GetSmallp(PipeFD));
       } else {
         DBPRINT(("Fork request failed."));
@@ -514,62 +515,43 @@ LispPTR Unix_handlecomm(LispPTR *args) {
 
       N_GETNUMBER(args[1], slot, bad);
 
-      DBPRINT(("Killing process in slot %d.\n", slot));
-
-      if (valid_slot(slot)) switch (UJ[slot].type) {
-          case UJSHELL:
-          case UJPROCESS:
-            /* First check to see it hasn't already died */
-            if (UJ[slot].status == -1) {
-              /* Kill the job */
-              kill(UJ[slot].PID, SIGKILL);
-              for (int i = 0; i < 10; i++) {
-                /* Waiting for the process to exit is possibly risky.
-                   Sending SIGKILL is always supposed to kill
-                   a process, but on very rare occurrences this doesn't
-                   happen because of a Unix kernel bug, usually a user-
-                   written device driver which hasn't been fully
-                   debugged.  So we time it out just be safe. */
-                if (UJ[slot].status != -1) break;
-                wait_for_comm_processes();
-                usleep(10);
-              }
-            }
-            break;
-          default: break;
-          }
-      else
-        return (ATOM_T);
-
+      DBPRINT(("Terminating process in slot %d.\n", slot));
+      if (!valid_slot(slot)) return (ATOM_T);
+      /* in all cases we need to close() the file descriptor */
+      close(slot);
       switch (UJ[slot].type) {
-        case UJUNUSED:
-          break;
-
-        case UJSHELL:
-          DBPRINT(("Kill 3 closing shell desc %d.\n", slot));
-          close(slot);
-          break;
-
-        case UJPROCESS:
-          DBPRINT(("Kill 3 closing process desc %d.\n", slot));
-          close(slot);
-          break;
-
-        case UJSOSTREAM:
-          DBPRINT(("Kill 3 closing stream socket desc %d.\n", slot));
-          close(slot);
-          break;
-
-        case UJSOCKET:
-          DBPRINT(("Kill 3 closing raw socket desc %d.\n", slot));
-          close(slot);
+      case UJSHELL:
+      case UJPROCESS:
+        /* wait for up to 0.1s for it to exit on its own after the close() */
+        for (int i = 0; i < 10; i++) {
+          wait_for_comm_processes();
+          if (UJ[slot].status != -1) break;
+          usleep(10000); printf("."); fflush(stdout);
+        }
+        /* check again before we terminate it */
+        if (UJ[slot].status != -1) break;
+        kill(UJ[slot].PID, SIGKILL);
+        for (int i = 0; i < 10; i++) {
+          /* Waiting for the process to exit is possibly risky.
+             Sending SIGKILL is always supposed to kill
+             a process, but on very rare occurrences this doesn't
+             happen because of a Unix kernel bug, usually a user-
+             written device driver which hasn't been fully
+             debugged.  So we time it out just be safe. */
+          wait_for_comm_processes();
+          usleep(10000);
+          if (UJ[slot].status != -1) break;
+        }
+        break;
+      case UJSOCKET:
+        if (UJ[slot].pathname) {
           DBPRINT(("Unlinking %s\n", UJ[slot].pathname));
-          if (UJ[slot].pathname) {
-            if (unlink(UJ[slot].pathname) < 0) perror("Kill 3 unlink");
-            free(UJ[slot].pathname);
-            UJ[slot].pathname = NULL;
-          }
-          break;
+          if (unlink(UJ[slot].pathname) < 0) perror("Kill 3 unlink");
+          free(UJ[slot].pathname);
+          UJ[slot].pathname = NULL;
+        }
+        break;
+      default: break;
       }
       UJ[slot].type = UJUNUSED;
       UJ[slot].PID = 0;