Document the purpose of the struct _block members.

diff --git a/Python/pyarena.c b/Python/pyarena.c
index 33261b4314856d2b04627232ed95860e8b7d984e..242ca1d67da604518c8c5a9d257b08fa47bd60c4 100644 (file)
--- a/Python/pyarena.c
+++ b/Python/pyarena.c
@@ -1,7 +1,7 @@
 #include "Python.h"
 #include "pyarena.h"
 
-/* A simple arena block structure
+/* A simple arena block structure.
 
    Measurements with standard library modules suggest the average
    allocation is about 20 bytes and that most compiles use a single
@@ -10,9 +10,26 @@
 
 #define DEFAULT_BLOCK_SIZE 8192
 typedef struct _block {
+       /* Total number of bytes owned by this block available to pass out.
+        * Read-only after initialization.  The first such byte starts at
+        * ab_mem.
+        */
        size_t ab_size;
+
+       /* Total number of bytes already passed out.  The next byte available
+        * to pass out starts at ab_mem + ab_offset.
+        */
        size_t ab_offset;
+
+       /* An arena maintains a singly-linked, NULL-terminated list of
+        * all blocks owned by the arena.  These are linked via the
+        * ab_next member.
+        */
        struct _block *ab_next;
+
+       /* Pointer to the first allocatable byte owned by this block.  Read-
+        * only after initialization.
+        */
        void *ab_mem;
 } block;