support Ruby 3.0.x

HEAP_PAGE_SIZE no longer estimates malloc overhead in Ruby 3.0.x,
but we can now rely on the GC::INTERNAL_CONSTANTS hash to access
the true value.

We also need to account for Ractors in 3.0+, and thus we need to
rely on thread-specific `ruby_current_ec' instead of process-wide
`ruby_current_execution_context_ptr' (which no longer exists in
3.0+).

Finally, the VM seems prone to making some small immortal
allocations in a few places we were not expecting in 2.7 and
earlier.  Account for that and loosen some exact checks to
account for it.

Tested on Ruby 3.0.3 and 3.0.4

1 files changed, 21 insertions, 4 deletions

diff --git a/ext/mwrap/mwrap.c b/ext/mwrap/mwrap.c
index 8592ea7..cd68eed 100644
--- a/ext/mwrap/mwrap.c
+++ b/ext/mwrap/mwrap.c
@@ -3,7 +3,7 @@
  * License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
  */
 #define _LGPL_SOURCE /* allows URCU to inline some stuff */
-#include <ruby/ruby.h>
+#include <ruby.h> /* defines HAVE_RUBY_RACTOR_H on 3.0+ */
 #include <ruby/thread.h>
 #include <ruby/io.h>
 #include <execinfo.h>
@@ -22,10 +22,24 @@
 #include <urcu/rculist.h>
 #include "jhash.h"
 
+#if __STDC_VERSION__ >= 201112
+#        define MWRAP_TSD _Thread_local
+#elif defined(__GNUC__)
+#        define MWRAP_TSD __thread
+#else
+#        error _Thread_local nor __thread supported
+#endif
+
 static ID id_uminus;
 const char *rb_source_location_cstr(int *line); /* requires 2.6.0dev */
 extern int __attribute__((weak)) ruby_thread_has_gvl_p(void);
+
+#ifdef HAVE_RUBY_RACTOR_H /* Ruby 3.0+ */
+extern MWRAP_TSD void * __attribute__((weak)) ruby_current_ec;
+#else /* Ruby 2.6-2.7 */
 extern void * __attribute__((weak)) ruby_current_execution_context_ptr;
+#        define ruby_current_ec ruby_current_execution_context_ptr
+#endif
 extern void * __attribute__((weak)) ruby_current_vm_ptr; /* for rb_gc_count */
 extern size_t __attribute__((weak)) rb_gc_count(void);
 extern VALUE __attribute__((weak)) rb_cObject;
@@ -40,9 +54,12 @@ static size_t total_bytes_inc, total_bytes_dec;
 /* match values in Ruby gc.c */
 #define HEAP_PAGE_ALIGN_LOG 14
 enum {
-        HEAP_PAGE_ALIGN = (1UL << HEAP_PAGE_ALIGN_LOG),
+        HEAP_PAGE_ALIGN = (1UL << HEAP_PAGE_ALIGN_LOG)
+#ifndef HEAP_PAGE_SIZE /* Ruby 2.6-2.7 only */
+        ,
         REQUIRED_SIZE_BY_MALLOC = (sizeof(size_t) * 5),
         HEAP_PAGE_SIZE = (HEAP_PAGE_ALIGN - REQUIRED_SIZE_BY_MALLOC)
+#endif
 };
 
 #define IS_HEAP_PAGE_BODY ((struct src_loc *)-1)
@@ -75,7 +92,7 @@ static int resolving_malloc;
         } \
 } while (0)
 
-static __thread size_t locating;
+static MWRAP_TSD size_t locating;
 static size_t generation;
 static size_t page_size;
 static struct cds_lfht *totals;
@@ -214,7 +231,7 @@ static char *int2str(int num, char *dst, size_t * size)
 static int has_ec_p(void)
 {
         return (ruby_thread_has_gvl_p() && ruby_current_vm_ptr &&
-                ruby_current_execution_context_ptr);
+                ruby_current_ec);
 }
 
 struct acc {