streams: put_buf and fill_buf become lower-level.

In this commit, the put_buf and fill_buf stream virtual
functions are changed to operate directly on a low-level
buffer, rather than a stream. This will allow these functions
to be used for improving the performance of I/O operations
that are not related to buffer objects.

* stream.h (struct strm_ops): Change type signature of put_buf
and fill_buf members. The lengths and iszes are ucnum.
The return value is ucnum. The buffer is passed as a pointer
and length, rather than a buffer object.

* stream.c (unimpl_put_buf, unimpl_fill_buf, generic_put_buf,
generic_fill_buf, stdio_put_buf, stdio_fill_buf,
delegate_put_buf, delegate_fill_buf): Adjust to
new interface.
(put_buf, fill_buf, fill_buf_adjust): Pull the poitner and
size from the buffer and pass those down to the virtual
functions rather than the buffer itself. Convert ucnum return
value to val.

* strudel.c (strudel_put_buf, strudel_get_buf): The struct
delegate interface doesn't change. The put-buf and fill-buf
methods still operate on buffer objects. To glue that with the
new low-level interface, we  use the init_borrowed_buf trick
that is was first used in ffi.c: temporary buf objects are
efficiently allocated on the stack, pointing to the same
memory that is coming down from the stream operation.

* txr.1: Document the new restrictions on the buf argument of
the put-buf and fill-buf stream delegate methods.
Since the buf not a heap object, it cannot be used after the
method returns.

1 files changed, 10 insertions, 4 deletions

diff --git a/strudel.c b/strudel.c
index 5aa4f67e..e36389b7 100644
--- a/strudel.c
+++ b/strudel.c
@@ -37,6 +37,8 @@
 #include "gc.h"
 #include "eval.h"
 #include "struct.h"
+#include "arith.h"
+#include "buf.h"
 #include "strudel.h"
 
 struct strudel_base { /* stru-ct del-egate :) */
@@ -120,20 +122,24 @@ static val strudel_unget_byte(val stream, int byte)
   return funcall2(meth, obj, num_fast(byte));
 }
 
-static val strudel_put_buf(val stream, val buf, cnum pos)
+static ucnum strudel_put_buf(val stream, mem_t *ptr, ucnum len, ucnum pos)
 {
   struct strudel_base *sb = coerce(struct strudel_base *, stream->co.handle);
+  obj_t buf_obj;
+  val buf = init_borrowed_buf(&buf_obj, unum(len), ptr);
   val obj = sb->obj;
   val meth = slot(obj, put_buf_s);
-  return funcall3(meth, obj, buf, num(pos));
+  return c_unum(funcall3(meth, obj, buf, num(pos)));
 }
 
-static val strudel_fill_buf(val stream, val buf, cnum pos)
+static ucnum strudel_fill_buf(val stream, mem_t *ptr, ucnum len, ucnum pos)
 {
   struct strudel_base *sb = coerce(struct strudel_base *, stream->co.handle);
+  obj_t buf_obj;
+  val buf = init_borrowed_buf(&buf_obj, unum(len), ptr);
   val obj = sb->obj;
   val meth = slot(obj, fill_buf_s);
-  return funcall3(meth, obj, buf, num(pos));
+  return c_unum(funcall3(meth, obj, buf, num(pos)));
 }
 
 static val strudel_close(val stream, val throw_on_error)