It looks like the 'scratch_buffer' could be useful to some programs
outside of glibc. But you cannot expect that a developer will dig
into lib/malloc/scratch_buffer.h, to read definitions full of __libc_
prefixed symbols and libc_hidden_proto declarations, and understand
what function names they can actually use.
So, I'm adding readable documentation for this module.
Paul: Note that the 'dynarray' documentation has the same problem.
Plus, it seems that some functions have a 'gl_' prefix and some
don't. Does this matter? Maybe it does not matter because
the contents of lib/malloc/dynarray.h is irrelevant and only
lib/malloc/dynarray-skeleton.c matters?
2021-02-21 Bruno Haible <br...@clisp.org>
scratch_buffer: Document the exported API.
* lib/scratch_buffer.h: Add comments, taken from
lib/malloc/scratch_buffer.h.
diff --git a/lib/scratch_buffer.h b/lib/scratch_buffer.h
index 603b0d6..f4b5f9e 100644
--- a/lib/scratch_buffer.h
+++ b/lib/scratch_buffer.h
@@ -19,6 +19,97 @@
#ifndef _GL_SCRATCH_BUFFER_H
#define _GL_SCRATCH_BUFFER_H
+/* Scratch buffers with a default stack allocation and fallback to
+ heap allocation. It is expected that this function is used in this
+ way:
+
+ struct scratch_buffer tmpbuf;
+ scratch_buffer_init (&tmpbuf);
+
+ while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
+ if (!scratch_buffer_grow (&tmpbuf))
+ return -1;
+
+ scratch_buffer_free (&tmpbuf);
+ return 0;
+
+ The allocation functions (scratch_buffer_grow,
+ scratch_buffer_grow_preserve, scratch_buffer_set_array_size) make
+ sure that the heap allocation, if any, is freed, so that the code
+ above does not have a memory leak. The buffer still remains in a
+ state that can be deallocated using scratch_buffer_free, so a loop
+ like this is valid as well:
+
+ struct scratch_buffer tmpbuf;
+ scratch_buffer_init (&tmpbuf);
+
+ while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
+ if (!scratch_buffer_grow (&tmpbuf))
+ break;
+
+ scratch_buffer_free (&tmpbuf);
+
+ scratch_buffer_grow and scratch_buffer_grow_preserve are guaranteed
+ to grow the buffer by at least 512 bytes. This means that when
+ using the scratch buffer as a backing store for a non-character
+ array whose element size, in bytes, is 512 or smaller, the scratch
+ buffer only has to grow once to make room for at least one more
+ element.
+*/
+
+/* Scratch buffer. Must be initialized with scratch_buffer_init
+ before its use. */
+struct scratch_buffer;
+
+/* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space
+ and BUFFER->length reflects the available space. */
+#if 0
+extern void scratch_buffer_init (struct scratch_buffer *buffer);
+#endif
+
+/* Deallocates *BUFFER (if it was heap-allocated). */
+#if 0
+extern void scratch_buffer_free (struct scratch_buffer *buffer);
+#endif
+
+/* Grow *BUFFER by some arbitrary amount. The buffer contents is NOT
+ preserved. Return true on success, false on allocation failure (in
+ which case the old buffer is freed). On success, the new buffer is
+ larger than the previous size. On failure, *BUFFER is deallocated,
+ but remains in a free-able state, and errno is set. */
+#if 0
+extern bool scratch_buffer_grow (struct scratch_buffer *buffer);
+#endif
+
+/* Like scratch_buffer_grow, but preserve the old buffer
+ contents on success, as a prefix of the new buffer. */
+#if 0
+extern bool scratch_buffer_grow_preserve (struct scratch_buffer *buffer);
+#endif
+
+/* Grow *BUFFER so that it can store at least NELEM elements of SIZE
+ bytes. The buffer contents are NOT preserved. Both NELEM and SIZE
+ can be zero. Return true on success, false on allocation failure
+ (in which case the old buffer is freed, but *BUFFER remains in a
+ free-able state, and errno is set). It is unspecified whether this
+ function can reduce the array size. */
+#if 0
+extern bool scratch_buffer_set_array_size (struct scratch_buffer *buffer,
+ size_t nelem, size_t size);
+#endif
+
+/* Return a copy of *BUFFER's first SIZE bytes as a heap-allocated block,
+ deallocating *BUFFER if it was heap-allocated. SIZE must be at
+ most *BUFFER's size. Return NULL (setting errno) on memory
+ exhaustion. */
+#if 0
+extern void *scratch_buffer_dupfree (struct scratch_buffer *buffer,
+ size_t size);
+#endif
+
+
+/* The implementation is imported from glibc. */
+
#include <libc-config.h>
#define __libc_scratch_buffer_dupfree gl_scratch_buffer_dupfree
