From dfebfa3c8c985ca7fdcc44026253d61d98089c95 Mon Sep 17 00:00:00 2001
From: Michael Santos <michael.santos@gmail.com>
Date: Wed, 12 Mar 2014 16:59:21 -0400
Subject: [PATCH] Try not to leak PID slots

Set a flag when a child exits, then free the slot when all the fd's
associated with the child have been marked as closed. Presumably this
should prevent the situation where a signal has occurred but there is
pending data on an fd. In this case, the parent would previously discard
the data and free the slot immediately.
---
 c_src/alcove.c | 27 +++++++++++++++++++++------
 c_src/alcove.h |  1 +
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/c_src/alcove.c b/c_src/alcove.c
index 83ff129..e363727 100644
--- a/c_src/alcove.c
+++ b/c_src/alcove.c
@@ -53,7 +53,8 @@ static ssize_t alcove_child_stdio(int fdin, pid_t pid, u_int16_t type);
 static ssize_t alcove_write(u_int16_t, ETERM *);
 static ssize_t alcove_read(int, void *, ssize_t);
 
-static int zero_pid(alcove_child_t *c, void *arg1, void *arg2);
+static int exited_pid(alcove_child_t *c, void *arg1, void *arg2);
+static int free_pid(alcove_child_t *c, void *arg1, void *arg2);
 static int set_pid(alcove_child_t *c, void *arg1, void *arg2);
 static int write_to_pid(alcove_child_t *c, void *arg1, void *arg2);
 static int read_from_pid(alcove_child_t *c, void *arg1, void *arg2);
@@ -130,13 +131,14 @@ alcove_ctl(alcove_state_t *ap)
                 case 0:
                     break;
                 default:
-                    ap->nchild--;
-                    (void)pid_foreach(ap, pid, NULL, NULL, pid_equal, zero_pid);
+                    (void)pid_foreach(ap, pid, NULL, NULL, pid_equal, exited_pid);
             }
 
             child_exited = 0;
         }
 
+        (void)pid_foreach(ap, 0, ap, NULL, pid_not_equal, free_pid);
+
         FD_ZERO(&rfds);
         FD_SET(STDIN_FILENO, &rfds);
 
@@ -414,15 +416,28 @@ pid_not_equal(pid_t p1, pid_t p2)
 }
 
     static int
-zero_pid(alcove_child_t *c, void *arg1, void *arg2)
+exited_pid(alcove_child_t *c, void *arg1, void *arg2)
 {
     (void)close(c->fdin);
     c->fdin = -1;
-    c->pid = 0;
-
+    c->exited = 1;
     return 0;
 }
 
+    static int
+free_pid(alcove_child_t *c, void *arg1, void *arg2)
+{
+    alcove_state_t *ap = arg1;
+
+    if (c->exited && c->fdout == -1 && c->fderr == -1) {
+            c->pid = 0;
+            c->exited = 0;
+            ap->nchild--;
+    }
+
+    return 1;
+}
+
     static int
 set_pid(alcove_child_t *c, void *arg1, void *arg2)
 {
diff --git a/c_src/alcove.h b/c_src/alcove.h
index 13ec52b..783edec 100644
--- a/c_src/alcove.h
+++ b/c_src/alcove.h
@@ -40,6 +40,7 @@ enum {
 
 typedef struct {
     pid_t pid;
+    int exited;
     int fdin;
     int fdout;
     int fderr;