Various additions and fixes.

src/lib9/atexit.c

@@ -0,0 +1,54 @@
+#include <u.h>
+#include <libc.h>
+
+#define	NEXIT	33
+
+static Lock onexlock;
+static struct
+{
+	void	(*f)(void);
+	int	pid;
+}onex[NEXIT];
+
+int
+atexit(void (*f)(void))
+{
+	int i;
+
+	lock(&onexlock);
+	for(i=0; i<NEXIT; i++)
+		if(onex[i].f == 0) {
+			onex[i].pid = getpid();
+			onex[i].f = f;
+			unlock(&onexlock);
+			return 1;
+		}
+	unlock(&onexlock);
+	return 0;
+}
+
+void
+atexitdont(void (*f)(void))
+{
+	int i, pid;
+
+	pid = getpid();
+	for(i=0; i<NEXIT; i++)
+		if(onex[i].f == f && onex[i].pid == pid)
+			onex[i].f = 0;
+}
+
+void
+exits(char *s)
+{
+	int i, pid;
+	void (*f)(void);
+
+	pid = getpid();
+	for(i = NEXIT-1; i >= 0; i--)
+		if((f = onex[i].f) && pid == onex[i].pid) {
+			onex[i].f = 0;
+			(*f)();
+		}
+	_exits(s);
+}