kernel: proc: Decrement proc count on exit

Previously, our process counter was monotonic (wuh oh!). We want to be
sure that it decrements when a process exits.

- Rename nthreads to g_nthreads as a global
- Atomically increment on enter and decrement on exit

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 11 insertions, 2 deletions

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 2c9e2e4..6b41cbd 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -30,6 +30,7 @@
 #include <sys/proc.h>
 #include <sys/sched.h>
 #include <sys/syslog.h>
+#include <sys/atomic.h>
 #include <sys/panic.h>
 #include <sys/filedesc.h>
 #include <sys/vnode.h>
@@ -44,6 +45,8 @@
 #define pr_trace(fmt, ...) kprintf("exit: " fmt, ##__VA_ARGS__)
 #define pr_error(...) pr_trace(__VA_ARGS__)
 
+extern volatile size_t g_nthreads;
+
 static void
 unload_td(struct proc *td)
 {
@@ -150,6 +153,9 @@ exit1(struct proc *td, int flags)
     td->flags |= PROC_EXITING;
     parent = td->parent;
 
+    /* We have one less process in the system! */
+    atomic_dec_64(&g_nthreads);
+
     /* If we have any children, kill them too */
     if (td->nleaves > 0) {
         TAILQ_FOREACH(procp, &td->leafq, leaf_link) {
diff --git a/sys/kern/kern_spawn.c b/sys/kern/kern_spawn.c
index fcaa194..37c3120 100644
--- a/sys/kern/kern_spawn.c
+++ b/sys/kern/kern_spawn.c
@@ -33,6 +33,7 @@
 #include <sys/mman.h>
 #include <sys/systm.h>
 #include <sys/errno.h>
+#include <sys/atomic.h>
 #include <sys/syslog.h>
 #include <sys/syscall.h>
 #include <sys/atomic.h>
@@ -47,7 +48,8 @@
 
 #define ARGVP_MAX (ARG_MAX / sizeof(void *))
 
-static volatile size_t nthreads = 0;
+static size_t next_pid = 1;
+volatile size_t g_nthreads = 0;
 
 /*
  * TODO: envp
@@ -166,7 +168,8 @@ spawn(struct proc *cur, void(*func)(void), void *p, int flags, struct proc **new
     newproc->mlgdr = mlgdr;
     newproc->flags |= PROC_WAITED;
 
-    newproc->pid = ++nthreads;
+    atomic_inc_64(&g_nthreads);
+    newproc->pid = next_pid++;
     signals_init(newproc);
     sched_enqueue_td(newproc);
     pid = newproc->pid;