From eb24df9749994d175a2de3b7fc0535abe46a7576 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sun, 13 Mar 2016 20:23:41 -0500
Subject: Split out _xexit() from xexit() and give sigatexit() multiple
 callbacks.

---
 lib/lib.c     | 17 +++++++++++++++--
 lib/lib.h     |  1 +
 lib/xwrap.c   | 25 ++++++++++++++++++++++---
 toys.h        |  1 +
 www/code.html | 19 +++++++++++++++++--
 5 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/lib/lib.c b/lib/lib.c
index 1c1f2248..200f77d6 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -757,11 +757,24 @@ void generic_signal(int sig)
   toys.signal = sig;
 }
 
-// Install the same handler on every signal that defaults to killing the process
+void exit_signal(int sig)
+{
+  toys.exitval = sig|128;
+  xexit();
+}
+
+// Install the same handler on every signal that defaults to killing the
+// process, and 
 void sigatexit(void *handler)
 {
+  struct arg_list *al = xmalloc(sizeof(struct arg_list));
   int i;
-  for (i=0; signames[i].num != SIGCHLD; i++) signal(signames[i].num, handler);
+
+  for (i=0; signames[i].num != SIGCHLD; i++)
+    signal(signames[i].num, exit_signal);
+  al->next = toys.xexit;
+  al->arg = handler;
+  toys.xexit = al;
 }
 
 // Convert name to signal number.  If name == NULL print names.
diff --git a/lib/lib.h b/lib/lib.h
index 917be0c1..b12a110b 100644
--- a/lib/lib.h
+++ b/lib/lib.h
@@ -96,6 +96,7 @@ void show_help(FILE *out);
 // xwrap.c
 void xstrncpy(char *dest, char *src, size_t size);
 void xstrncat(char *dest, char *src, size_t size);
+void _xexit(void) noreturn;
 void xexit(void) noreturn;
 void *xmalloc(size_t size);
 void *xzalloc(size_t size);
diff --git a/lib/xwrap.c b/lib/xwrap.c
index 78103555..0b1ab8e9 100644
--- a/lib/xwrap.c
+++ b/lib/xwrap.c
@@ -28,13 +28,32 @@ void xstrncat(char *dest, char *src, size_t size)
   strcpy(dest+len, src);
 }
 
+// We replaced exit(), _exit(), and atexit() with xexit(), _xexit(), and
+// sigatexit(). This gives _xexit() the option to siglongjmp(toys.rebound, 1)
+// instead of exiting, lets xexit() report stdout flush failures to stderr
+// and change the exit code to indicate error, lets our toys.exit function
+// change happen for signal exit paths and lets us remove the functions
+// after we've called them.
+
+void _xexit(void)
+{
+  if (toys.rebound) siglongjmp(*toys.rebound, 1);
+
+  _exit(toys.exitval);
+}
+
 void xexit(void)
 {
-  if (toys.rebound) longjmp(*toys.rebound, 1);
+  // Call toys.xexit functions in reverse order added.
+  while (toys.xexit) {
+    // This is typecasting xexit->arg to a function pointer,then calling it.
+    ((void (*)(void))(toys.xexit->arg))();
+
+    free(llist_pop(&toys.xexit));
+  }
   if (fflush(NULL) || ferror(stdout))
     if (!toys.exitval) perror_msg("write");
-
-  exit(toys.exitval);
+  _xexit();
 }
 
 // Die unless we can allocate memory.
diff --git a/toys.h b/toys.h
index 8a29730b..414f439c 100644
--- a/toys.h
+++ b/toys.h
@@ -113,6 +113,7 @@ extern struct toy_context {
 
   // This is at the end so toy_init() doesn't zero it.
   jmp_buf *rebound;        // longjmp here instead of exit when do_rebound set
+  struct arg_list *xexit;  // atexit() functions for xexit(), set by sigatexit()
   void *stacktop;          // nested toy_exec() call count, or 0 if vforked
 } toys;
 
diff --git a/www/code.html b/www/code.html
index 7e15e181..c133611c 100644
--- a/www/code.html
+++ b/www/code.html
@@ -632,13 +632,28 @@ itoa().</p>
 errors, to eliminate common error checking. This prints an error message
 and the strerror() string for the errno encountered.</p>
 
-<p>You can intercept this exit by assigning a setjmp/longjmp buffer to
+<p>We replaced exit(), _exit(), and atexit() with xexit(), _xexit(), and
+sigatexit(). This gives _xexit() the option to siglongjmp(toys.rebound, 1)
+instead of exiting, lets xexit() report stdout flush failures to stderr
+and change the exit code to indicate error, lets our toys.exit function
+change happen for signal exit paths and lets us remove the functions
+after we've called them.</p>
+
+<p>You can intercept our exit by assigning a setjmp/longjmp buffer to
 toys.rebound (set it back to zero to restore the default behavior).
 If you do this, cleaning up resource leaks is your problem.</p>
 
 <ul>
 <li><b>void xstrncpy(char *dest, char *src, size_t size)</b></li>
-<li><b>void xexit(void)</b></li>
+<li><p><b><p>void _xexit(void)</b></p>
+<p>Calls siglongjmp(toys.rebound, 1), or else _exit(toys.exitval). This
+lets you ignore errors with the NO_EXIT() macro wrapper, or intercept
+them with WOULD_EXIT().</p>
+<li><b><p>void xexit(void)</b></p>
+<p>Calls toys.xexit functions (if any) and flushes stdout/stderr (reporting
+failure to write to stdout both to stderr and in the exit code), then
+calls _xexit().</p>
+</li>
 <li><b>void *xmalloc(size_t size)</b></li>
 <li><b>void *xzalloc(size_t size)</b></li>
 <li><b>void *xrealloc(void *ptr, size_t size)</b></li>
-- 
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