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, 4 insertions, 0 deletions

diff --git a/HOWTO/INSTALL.md b/HOWTO/INSTALL.md
index 8632f46264..551ecdd224 100644
--- a/HOWTO/INSTALL.md
+++ b/HOWTO/INSTALL.md
@@ -429,6 +429,10 @@ Some of the available `configure` options are:
     and **not supported**. This functionality **will** be subject to backward
     incompatible changes. Note that you should **not** enable the dirty scheduler
     functionality on production systems. It is only provided for testing.
+    This switch also imply `--enable-new-purge-strategy` (see below).
+*   `--enable-new-purge-strategy` - Enable the purge strategy that will be
+    introduced in ERTS version 9.0 (OTP 20). Note that this switch will be
+    removed in OTP 20.
 
 If you or your system has special requirements please read the `Makefile` for
 additional configuration information.