Thread specific storage APIs

This patch introduces thread specific storage APIs
for tools which use `rb_internal_thread_event_hook` APIs.

* `rb_internal_thread_specific_key_create()` to create a tool specific
  thread local storage key and allocate the storage if not available.
* `rb_internal_thread_specific_set()` sets a data to thread and tool
  specific storage.
* `rb_internal_thread_specific_get()` gets a data in thread and tool
  specific storage.

Note that `rb_internal_thread_specific_get|set(thread_val, key)`
can be called without GVL and safe for async signal and safe for
multi-threading (native threads). So you can call it in any internal
thread event hooks. Further more you can call it from other native
threads. Of course `thread_val` should be living while accessing the
data from this function.

Note that you should not forget to clean up the set data.

1 files changed, 1 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index fcac71b2e5..cd720fd8cf 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1152,6 +1152,7 @@ typedef struct rb_thread_struct {
 
     /* misc */
     VALUE name;
+    void **specific_storage;
 
     struct rb_ext_config ext_config;
 } rb_thread_t;