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, 6 insertions, 27 deletions

diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 503ef5c2f6..2ad5f3b4d5 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -49,7 +49,6 @@
 #include <sys/ioctl.h>
 #endif
 
-#define NEED_CHILD_SETUP_DEFINES
 #define ERTS_WANT_BREAK_HANDLING
 #define ERTS_WANT_GOT_SIGUSR1
 #define WANT_NONBLOCKING    /* must define this to pull in defs from sys.h */
@@ -93,6 +92,7 @@ extern void erts_sys_init_float(void);
 
 extern void erl_crash_dump(char* file, int line, char* fmt, ...);
 
+
 #ifdef DEBUG
 static int debug_log = 0;
 #endif
@@ -122,6 +122,7 @@ static void smp_sig_notify(char c);
 static int sig_notify_fds[2] = {-1, -1};
 
 static int sig_suspend_fds[2] = {-1, -1};
+#define ERTS_SYS_SUSPEND_SIGNAL SIGUSR2
 
 #endif
 
@@ -307,9 +308,10 @@ MALLOC_USE_HASH(1);
 #ifdef USE_THREADS
 
 #ifdef ERTS_THR_HAVE_SIG_FUNCS
+
 /*
  * Child thread inherits parents signal mask at creation. In order to
- * guarantee that the main thread will receive all SIGINT, SIGCHLD, and
+ * guarantee that the main thread will receive all SIGINT, and
  * SIGUSR1 signals sent to the process, we block these signals in the
  * parent thread when creating a new thread.
  */
@@ -405,7 +407,6 @@ erts_sys_pre_init(void)
 #ifdef ERTS_THR_HAVE_SIG_FUNCS
     sigemptyset(&thr_create_sigmask);
     sigaddset(&thr_create_sigmask, SIGINT);   /* block interrupt */
-    sigaddset(&thr_create_sigmask, SIGCHLD);  /* block child signals */
     sigaddset(&thr_create_sigmask, SIGUSR1);  /* block user defined signal */
 #endif
 
@@ -1010,7 +1011,6 @@ erts_sys_unsetenv(char *key)
 void
 sys_init_io(void)
 {
-
 }
 
 #if (0) /* unused? */
@@ -1204,7 +1204,6 @@ erl_debug(char* fmt, ...)
 
 #endif /* DEBUG */
 
-
 /*
  * Called from schedule() when it runs out of runnable processes,
  * or when Erlang code has performed INPUT_REDUCTIONS reduction
@@ -1213,15 +1212,11 @@ erl_debug(char* fmt, ...)
 void
 erl_sys_schedule(int runnable)
 {
-#ifdef ERTS_SMP
     ERTS_CHK_IO(!runnable);
-#else
-    ERTS_CHK_IO(runnable ? 0 : !check_children());
-#endif
     ERTS_SMP_LC_ASSERT(!erts_thr_progress_is_blocking());
-    (void) check_children();
 }
 
+
 #ifdef ERTS_SMP
 
 static erts_smp_tid_t sig_dispatcher_tid;
@@ -1246,10 +1241,6 @@ smp_sig_notify(char c)
 static void *
 signal_dispatcher_thread_func(void *unused)
 {
-#if !CHLDWTHR
-    int initialized = 0;
-    int notify_check_children = 0;
-#endif
 #ifdef ERTS_ENABLE_LOCK_CHECK
     erts_lc_set_thread_name("signal_dispatcher");
 #endif
@@ -1287,19 +1278,7 @@ signal_dispatcher_thread_func(void *unused)
 	     */
 	    switch (buf[i]) {
 	    case 0: /* Emulator initialized */
-#if !CHLDWTHR
-		initialized = 1;
-		if (!notify_check_children)
-#endif
-		    break;
-#if !CHLDWTHR
-	    case 'C': /* SIGCHLD */
-		if (initialized)
-		    erts_smp_notify_check_children_needed();
-		else
-		    notify_check_children = 1;
-		break;
-#endif
+                break;
 	    case 'I': /* SIGINT */
 		break_requested();
 		break;