[ruby] simplify shutdown; remove unnecessary attempts at grpc_shutdown (#33674)

So far, we've structured global C-core init/shutdown as follows:
1) every grpc-ruby object calls `grpc_init` when allocated, and
`grpc_shutdown` when finalized
2) grpc-ruby background threads are each wrapped in a
`grpc_init/shutdown` pair - for example see
b32d94de05/src/ruby/ext/grpc/rb_event_thread.c (L122)
and
b32d94de05/src/ruby/ext/grpc/rb_event_thread.c (L136)

But because ruby doesn't join ruby threads when the process is
terminating, the `init/shutdown` pairs in 2) are always left open. I.e.,
thus far we have never been invoking the final call to `grpc_shutdown`
which actually does C-core global shutdown. Thus our calls to
`grpc_shutdown` are useless.

So we might as well keep things simple and not even attempt to call
`grpc_shutdown`. Now we just call `grpc_init` before using C-core, and
then never even attempt global shutdown (in non-forking situations).

As a bonus, this fixes the issue with the event thread's
`grpc_ruby_init` racing with `prefork` that is mentioned in
https://github.com/grpc/grpc/pull/33666

src/ruby/ext/grpc/rb_call_credentials.c

@@ -193,7 +193,6 @@ static void grpc_rb_call_credentials_free_internal(void* p) {
 /* Destroys the credentials instances. */
 static void grpc_rb_call_credentials_free(void* p) {
   grpc_rb_call_credentials_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Protects the mark object from GC */

src/ruby/ext/grpc/rb_channel.c

@@ -169,10 +169,7 @@ static void grpc_rb_channel_free_internal(void* p) {
 }
 
 /* Destroys Channel instances. */
-static void grpc_rb_channel_free(void* p) {
-  grpc_rb_channel_free_internal(p);
-  grpc_ruby_shutdown();
-}
+static void grpc_rb_channel_free(void* p) { grpc_rb_channel_free_internal(p); }
 
 /* Protects the mark object from GC */
 static void grpc_rb_channel_mark(void* p) {
@@ -759,10 +756,8 @@ static VALUE run_poll_channels_loop(VALUE arg) {
   gpr_log(
       GPR_DEBUG,
       "GRPC_RUBY: run_poll_channels_loop - create connection polling thread");
-  grpc_ruby_init();
   rb_thread_call_without_gvl(run_poll_channels_loop_no_gil, NULL,
                              run_poll_channels_loop_unblocking_func, NULL);
-  grpc_ruby_shutdown();
   return Qnil;
 }
 

src/ruby/ext/grpc/rb_channel_credentials.c

@@ -63,7 +63,6 @@ static void grpc_rb_channel_credentials_free_internal(void* p) {
 /* Destroys the credentials instances. */
 static void grpc_rb_channel_credentials_free(void* p) {
   grpc_rb_channel_credentials_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Protects the mark object from GC */

src/ruby/ext/grpc/rb_compression_options.c

@@ -70,7 +70,6 @@ static void grpc_rb_compression_options_free_internal(void* p) {
  * wrapped grpc compression options. */
 static void grpc_rb_compression_options_free(void* p) {
   grpc_rb_compression_options_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Ruby recognized data type for the CompressionOptions class. */

src/ruby/ext/grpc/rb_event_thread.c

@@ -119,7 +119,6 @@ static void grpc_rb_event_unblocking_func(void* arg) {
 static VALUE grpc_rb_event_thread(VALUE arg) {
   grpc_rb_event* event;
   (void)arg;
-  grpc_ruby_init();
   while (true) {
     event = (grpc_rb_event*)rb_thread_call_without_gvl(
         grpc_rb_wait_for_event_no_gil, NULL, grpc_rb_event_unblocking_func,
@@ -133,7 +132,6 @@ static VALUE grpc_rb_event_thread(VALUE arg) {
     }
   }
   grpc_rb_event_queue_destroy();
-  grpc_ruby_shutdown();
   return Qnil;
 }
 

src/ruby/ext/grpc/rb_grpc.c

@@ -355,23 +355,6 @@ void grpc_ruby_init() {
           g_enable_fork_support, g_grpc_ruby_init_count++);
 }
 
-void grpc_ruby_shutdown() {
-  GPR_ASSERT(g_grpc_ruby_init_count > 0);
-  // Avoid calling grpc_shutdown if we've enabled forking, in order to
-  // avoid the hypothetical case where grpc_shutdown spawns a detached thread
-  // that remains alive at fork, potentially causing undefined behavior in
-  // the child process.
-  if (g_enable_fork_support) return;
-  // TODO(apolcyn): call, or don't call, grpc_shutdown() unconditionally
-  // at this point? So far we've been skipping when forking without fork
-  // support enabled.
-  if (grpc_ruby_initial_pid()) grpc_shutdown();
-  gpr_log(
-      GPR_DEBUG,
-      "GRPC_RUBY: grpc_ruby_shutdown - prev g_grpc_ruby_init_count:%" PRId64,
-      g_grpc_ruby_init_count--);
-}
-
 // fork APIs, useable on linux with env var: GRPC_ENABLE_FORK_SUPPORT=1
 //
 // Must be called once and only once before forking. Must be called on the

src/ruby/ext/grpc/rb_grpc.h

@@ -80,6 +80,4 @@ void grpc_rb_fork_unsafe_end();
 
 void grpc_ruby_init();
 
-void grpc_ruby_shutdown();
-
 #endif /* GRPC_RB_H_ */

src/ruby/ext/grpc/rb_server.c

@@ -106,10 +106,7 @@ static void grpc_rb_server_free_internal(void* p) {
 }
 
 /* Destroys server instances. */
-static void grpc_rb_server_free(void* p) {
-  grpc_rb_server_free_internal(p);
-  grpc_ruby_shutdown();
-}
+static void grpc_rb_server_free(void* p) { grpc_rb_server_free_internal(p); }
 
 static const rb_data_type_t grpc_rb_server_data_type = {
     "grpc_server",

src/ruby/ext/grpc/rb_server_credentials.c

@@ -62,7 +62,6 @@ static void grpc_rb_server_credentials_free_internal(void* p) {
 /* Destroys the server credentials instances. */
 static void grpc_rb_server_credentials_free(void* p) {
   grpc_rb_server_credentials_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Protects the mark object from GC */

src/ruby/ext/grpc/rb_xds_channel_credentials.c

@@ -62,7 +62,6 @@ static void grpc_rb_xds_channel_credentials_free_internal(void* p) {
 /* Destroys the credentials instances. */
 static void grpc_rb_xds_channel_credentials_free(void* p) {
   grpc_rb_xds_channel_credentials_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Protects the mark object from GC */

src/ruby/ext/grpc/rb_xds_server_credentials.c

@@ -63,7 +63,6 @@ static void grpc_rb_xds_server_credentials_free_internal(void* p) {
 /* Destroys the server credentials instances. */
 static void grpc_rb_xds_server_credentials_free(void* p) {
   grpc_rb_xds_server_credentials_free_internal(p);
-  grpc_ruby_shutdown();
 }
 
 /* Protects the mark object from GC */