[ruby-core:28952] Re: st.c: pool allocator for tables and entries

Aaron Patterson <[e-mail]> wrote:
> On Wed, Mar 24, 2010 at 07:43:56PM +0900, NARUSE, Yui wrote:
> > (2010/03/22 17:05), Eric Wong wrote:
> > >This assumes st.c is only called inside GVL, and GVL == GIL which is
> > >true these days in 1.9.1 and trunk.
> > 
> > st.c is used not only from GC, but by other extensions.
> > 
> > I don't know whether st.h is public API or not.
> > But if a library uses st_table in multi thread way,
> > it will break when st_table become thread unsafe.
> 
> FWIW, Nokogiri uses st.h.

st.h seems public, at least there are several extensions that use it,
too (json, rcov, ruby-prof) but very few of them release GVL, so they
should all be safe.

Combining thread-safety good malloc performance is a lot of work, I
would just defer to the malloc implementation (like tcmalloc) if
thread-safety is a concern.

I not sure if this patch series is suitable for ruby itself, which
is why I'm putting them here first for discussion (and not Redmine).

diff --git a/st.c b/st.c
index 54ebee9..c9a5bba 100644
--- a/st.c
+++ b/st.c
@@ -7,6 +7,7 @@
 #include "st.h"
 #else
 #include "ruby/ruby.h"
+#include "vm_core.h"
 #endif
 
 #include <stdio.h>
@@ -38,6 +39,22 @@ struct st_table_entry {
      *
      */
 
+/*
+ * assume USE_VALUE_CACHE means we care about thread-safety
+ */
+#if USE_VALUE_CACHE
+/* thread-safety, defer to slower malloc() implementation */
+#define DEFINE_ALLOC_POOL(name,type,size) \
+static inline type *alloc_##name(void) \
+{ \
+    return ruby_xmalloc(sizeof(type)); \
+} \
+static inline void release_##name(void *ptr) \
+{ \
+    ruby_xfree(ptr); \
+}
+#else
+/* not thread-safe, but faster if st.h users don't release GVL */
 #if __GNUC__ >= 3
 #define UNLIKELY(x) (__builtin_expect((x), 0))
 #else /* __GNUC__ >= 3 */
@@ -83,6 +100,7 @@ static void release_##name(void *ptr) \
     tmp->as.next = name##_head ? name##_head : NULL; \
     name##_head = tmp; \
 }
+#endif
 
 DEFINE_ALLOC_POOL(entry, struct st_table_entry, 0x2000);
 DEFINE_ALLOC_POOL(table, struct st_table, 0x2000);
-- 
Eric Wong