From: Eric Wong <normalperson@...>
Date: 2015-08-10T18:37:12+00:00
Subject: [ruby-core:70317] Re: [ruby-cvs:58640] nobu:r51492 (trunk): node.c: NODE_ALLOCA for ALLOCV

Nobuyoshi Nakada <nobu@ruby-lang.org> wrote:
> On 2015/08/06 4:11, Eric Wong wrote:
> > Besides possible backwards compatibility, can we drop volatile
> > from rb_alloc_tmp_buffer and rb_free_tmp_buffer?  volatile
> > seems unnecessary since we call rb_free_tmp_buffer anyways.
> 
> It doesn't force the buffer variable to be `volatile`, but just allow.

Right, but many current use of volatile variables is wrong and other
APIs (PRI*VALUE or RB_GC_GUARD) are better instead.

Better to warn and avoid volatile instead of perpetuating it:

diff --git a/array.c b/array.c
index 27b6325..d08e2f5 100644
--- a/array.c
+++ b/array.c
@@ -4982,7 +4982,7 @@ rb_ary_permutation(int argc, VALUE *argv, VALUE ary)
 	}
     }
     else {             /* this is the general case */
-	volatile VALUE t0;
+	VALUE t0;
 	long *p = ALLOCV_N(long, t0, r+roomof(n, sizeof(long)));
 	char *used = (char*)(p + r);
 	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
@@ -5073,7 +5073,7 @@ rb_ary_combination(VALUE ary, VALUE num)
     }
     else {
 	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
-	volatile VALUE t0;
+	VALUE t0;
 	long *stack = ALLOCV_N(long, t0, n+1);
 
 	RBASIC_CLEAR_CLASS(ary0);
@@ -5178,7 +5178,7 @@ rb_ary_repeated_permutation(VALUE ary, VALUE num)
 	}
     }
     else {             /* this is the general case */
-	volatile VALUE t0;
+	VALUE t0;
 	long *p = ALLOCV_N(long, t0, r * sizeof(long));
 	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
 	RBASIC_CLEAR_CLASS(ary0);
@@ -5274,7 +5274,7 @@ rb_ary_repeated_combination(VALUE ary, VALUE num)
 	/* yield nothing */
     }
     else {
-	volatile VALUE t0;
+	VALUE t0;
 	long *p = ALLOCV_N(long, t0, n);
 	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
 	RBASIC_CLEAR_CLASS(ary0);
diff --git a/gc.c b/gc.c
index a3af6fe..44080ec 100644
--- a/gc.c
+++ b/gc.c
@@ -7767,7 +7767,7 @@ ruby_mimfree(void *ptr)
 }
 
 void *
-rb_alloc_tmp_buffer(volatile VALUE *store, long len)
+rb_alloc_tmp_buffer(VALUE *store, long len)
 {
     NODE *s;
     long cnt;
@@ -7786,7 +7786,7 @@ rb_alloc_tmp_buffer(volatile VALUE *store, long len)
 }
 
 void
-rb_free_tmp_buffer(volatile VALUE *store)
+rb_free_tmp_buffer(VALUE *store)
 {
     VALUE s = ATOMIC_VALUE_EXCHANGE(*store, 0);
     if (s) {
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 01b3c2e..d853fca 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1429,8 +1429,8 @@ rb_num2char_inline(VALUE x)
 
 #define ALLOCA_N(type,n) ((type*)alloca(sizeof(type)*(n)))
 
-void *rb_alloc_tmp_buffer(volatile VALUE *store, long len) RUBY_ATTR_ALLOC_SIZE((2));
-void rb_free_tmp_buffer(volatile VALUE *store);
+void *rb_alloc_tmp_buffer(VALUE *store, long len) RUBY_ATTR_ALLOC_SIZE((2));
+void rb_free_tmp_buffer(VALUE *store);
 /* allocates _n_ bytes temporary buffer and stores VALUE including it
  * in _v_.  _n_ may be evaluated twice. */
 #ifdef C_ALLOCA

-- 
EW