Fix purge of code

Ensure that we cannot get any dangling pointers into code that
has been purged. This is done by a two phase purge. At first
phase all fun entries pointing into the code to purge are marked
for purge. All processes trying to call these funs will be suspended
and by this we avoid getting new direct references into the code.
When all processes has been checked, these processes are resumed.

The new purge strategy now also completely ignore the existence of
indirect references to the code (funs). If such exist, they will
cause bad fun exceptions to the caller, but will not prevent a
soft purge or cause a kill of a process having such live references
during a hard purge. This since it is impossible to give any
guarantees that no processes in the system have such indirect
references. Even when the system is completely clean from such
references, new ones can appear via distribution and/or disk.

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/kernel/doc/src/code.xml b/lib/kernel/doc/src/code.xml
index d3611d6a03..21f8a2d54a 100644
--- a/lib/kernel/doc/src/code.xml
+++ b/lib/kernel/doc/src/code.xml
@@ -651,6 +651,11 @@ ok = code:finish_loading(Prepared),
         <p>Purges the code for <c><anno>Module</anno></c>, that is, removes code
           marked as old. If some processes still linger in the old code,
           these processes are killed before the code is removed.</p>
+	<note><p>As of ERTS version 9.0, a process is only considered
+	to be lingering in the code if it has direct references to the code.
+	For more information see documentation of
+	<seealso marker="erts:erlang#check_process_code/3"><c>erlang:check_process_code/3</c></seealso>,
+	which is used in order to determine this.</p></note>
         <p>Returns <c>true</c> if successful and any process is needed to
           be killed, otherwise <c>false</c>.</p>
       </desc>
@@ -661,6 +666,11 @@ ok = code:finish_loading(Prepared),
       <desc>
         <p>Purges the code for <c><anno>Module</anno></c>, that is, removes code
           marked as old, but only if no processes linger in it.</p>
+	<note><p>As of ERTS version 9.0, a process is only considered
+	to be lingering in the code if it has direct references to the code.
+	For more information see documentation of
+	<seealso marker="erts:erlang#check_process_code/3"><c>erlang:check_process_code/3</c></seealso>,
+	which is used in order to determine this.</p></note>
         <p>Returns <c>false</c> if the module cannot be purged because
           of processes lingering in old code, otherwise <c>true</c>.</p>
       </desc>