variable.c: additional locking around autoload

[ruby-core:70075] [ruby-core:71239] [Bug #11384] Note: this open-coding locking method may go into rb_mutex/rb_thread_shield types. It is smaller and simpler and based on the wait queue implementation of the Linux kernel. When/if we get rid of GVL, native mutexes may be used as-is. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52332 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: normal

ChangeLog

@@ -1,3 +1,8 @@
+Thu Oct 29 08:48:05 2015 Eric Wong <e@80x24.org>
+
+* variable.c: additional locking around autoload
+ [ruby-core:70075] [ruby-core:71239] [Bug #11384]
+
 Wed Oct 29 00:39:50 2015 Naohisa Goto <ngotogenome@gmail.com>
 
 * test/rubygems/test_gem_commands_server_command.rb

variable.c

@@ -16,6 +16,7 @@
 #include "ruby/util.h"
 #include "constant.h"
 #include "id.h"
+#include "ccan/list/list.h"
 
 st_table *rb_global_tbl;
 static ID autoload, classpath, tmp_classpath, classid;
@@ -1896,6 +1897,7 @@ struct autoload_data_i {
  int safe_level;
  VALUE thread;
  VALUE value;
+ struct list_head waitq_head; /* links autoload_state.waitq_node */
 };
 
 static void
@@ -2077,20 +2079,71 @@ autoload_const_set(VALUE arg)
  return 0;/* ignored */
 }
 
+/* this is on the thread stack, not heap */
+struct autoload_state {
+ struct autoload_data_i *ele;
+ VALUE mod;
+ VALUE result;
+ ID id;
+ struct list_node waitq_node; /* links autoload_data_i.waitq_head */
+ VALUE waiting_th;
+};
+
 static VALUE
 autoload_require(VALUE arg)
 {
- struct autoload_data_i *ele = (struct autoload_data_i *)arg;
- return rb_funcall(rb_vm_top_self(), rb_intern("require"), 1, ele->feature);
+ struct autoload_state *state = (struct autoload_state *)arg;
+
+ /* this may release GVL and switch threads: */
+ state->result = rb_funcall(rb_vm_top_self(), rb_intern("require"), 1,
+ state->ele->feature);
+
+ return state->result;
 }
 
 static VALUE
 autoload_reset(VALUE arg)
 {
- struct autoload_data_i *ele = (struct autoload_data_i *)arg;
- if (ele->thread == rb_thread_current()) {
-ele->thread = Qnil;
+ struct autoload_state *state = (struct autoload_state *)arg;
+ int need_wakeups = 0;
+
+ if (state->ele->thread == rb_thread_current()) {
+need_wakeups = 1;
+state->ele->thread = Qnil;
+ }
+
+ /* At the last, move a value defined in autoload to constant table */
+ if (RTEST(state->result) && state->ele->value != Qundef) {
+int safe_backup;
+struct autoload_const_set_args args;
+
+args.mod = state->mod;
+args.id = state->id;
+args.value = state->ele->value;
+safe_backup = rb_safe_level();
+rb_set_safe_level_force(state->ele->safe_level);
+rb_ensure(autoload_const_set, (VALUE)&args,
+ reset_safe, (VALUE)safe_backup);
+ }
+
+ /* wakeup any waiters we had */
+ if (need_wakeups) {
+struct autoload_state *cur, *nxt;
+
+list_for_each_safe(&state->ele->waitq_head, cur, nxt, waitq_node) {
+ VALUE th = cur->waiting_th;
+
+ cur->waiting_th = Qfalse;
+ list_del(&cur->waitq_node);
+
+ /*
+ * cur is stored on the stack of cur->waiting_th,
+ * do not touch cur after waking up waiting_th
+ */
+ rb_thread_wakeup_alive(th);
+}
  }
+
  return 0;/* ignored */
 }
 
@@ -2100,6 +2153,7 @@ rb_autoload_load(VALUE mod, ID id)
  VALUE load, result;
  const char *loading = 0, *src;
  struct autoload_data_i *ele;
+ struct autoload_state state;
 
  if (!autoload_defined_p(mod, id)) return Qfalse;
  load = check_autoload_required(mod, id, &loading);
@@ -2111,26 +2165,35 @@ rb_autoload_load(VALUE mod, ID id)
  if (!(ele = check_autoload_data(load))) {
 return Qfalse;
  }
+
+ state.ele = ele;
+ state.mod = mod;
+ state.id = id;
  if (ele->thread == Qnil) {
 ele->thread = rb_thread_current();
+
+/*
+ * autoload_reset will wake up any threads added to this
+ * iff the GVL is released during autoload_require
+ */
+list_head_init(&ele->waitq_head);
  }
+ else {
+state.waiting_th = rb_thread_current();
+list_add_tail(&ele->waitq_head, &state.waitq_node);
+/*
+ * autoload_reset in other thread will resume us and remove us
+ * from the waitq list
+ */
+do {
+ rb_thread_sleep_deadly();
+} while (state.waiting_th != Qfalse);
+ }
+
  /* autoload_data_i can be deleted by another thread while require */
- result = rb_ensure(autoload_require, (VALUE)ele, autoload_reset, (VALUE)ele);
+ result = rb_ensure(autoload_require, (VALUE)&state,
+ autoload_reset, (VALUE)&state);
 
- if (RTEST(result)) {
-/* At the last, move a value defined in autoload to constant table */
-if (ele->value != Qundef) {
- int safe_backup;
- struct autoload_const_set_args args;
- args.mod = mod;
- args.id = id;
- args.value = ele->value;
- safe_backup = rb_safe_level();
- rb_set_safe_level_force(ele->safe_level);
- rb_ensure(autoload_const_set, (VALUE)&args,
- reset_safe, (VALUE)safe_backup);
-}
- }
  RB_GC_GUARD(load);
  return result;
 }