erts: Create forker process for spawn driver

Instead of forking from the beam process, we create a separate
process in which all forks are done. This has several advantages:

1) performance:
  * don't have to close all fd's in the world
  * fork only has to copy stuff from a small process
  * work is done in a completely seperate process
  * a 3x performance increase has been measured,
    can be made even greater (10x) if we cache the
    environment in child setup

2) stability
  * the exec is done in another process than beam, which means that
    if the file that we exec to is on an nfs that is not available
    right now we will not block a scheduler until the nfs returns.

3) simplicity
  * don't have to deal with SIGCHLD in the erts

Unfortunately, this solution also implies some badness.

1) There will always be a seperate process running together with
   beam on unix. This could be confusing and undesirable.
2) We have to transfer the entire environment to child_setup
   for each command.

OTP-13088

1 files changed, 1 insertions, 0 deletions

diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index b4d02dd1dd..4352d5758b 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1322,6 +1322,7 @@ extern void erts_match_prog_foreach_offheap(Binary *b,
 
 extern erts_driver_t vanilla_driver;
 extern erts_driver_t spawn_driver;
+extern erts_driver_t forker_driver;
 extern erts_driver_t fd_driver;
 
 int erts_beam_jump_table(void);