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, 9 deletions

diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index 34011147d9..522d899c94 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -61,15 +61,6 @@
 #  define NO_FPE_SIGNALS
 #endif
 
-#ifdef DISABLE_CHILD_WAITER_THREAD
-#undef ENABLE_CHILD_WAITER_THREAD
-#endif
-
-#if defined(ERTS_SMP) && !defined(DISABLE_CHILD_WAITER_THREAD)
-#undef ENABLE_CHILD_WAITER_THREAD
-#define ENABLE_CHILD_WAITER_THREAD 1
-#endif
-
 #define ERTS_I64_LITERAL(X) X##LL
 
 #if defined (__WIN32__)
@@ -731,6 +722,7 @@ void erts_sys_main_thread(void);
 extern int erts_sys_prepare_crash_dump(int secs);
 extern void erts_sys_pre_init(void);
 extern void erl_sys_init(void);
+extern void erl_sys_late_init(void);
 extern void erl_sys_args(int *argc, char **argv);
 extern void erl_sys_schedule(int);
 void sys_tty_reset(int);