Add emulate the per-thread memory pool on Unix to the TODO

p4raw-id: //depot/perl@25439

1 files changed, 31 insertions, 0 deletions

diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index e315cd3023..0caa728164 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -273,6 +273,37 @@ anyone feeling like exercising their skill with coverage and profiling tools
 might want to determine what ops I<really> are the most commonly used. And in
 turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
 
+=head2 emulate the per-thread memory pool on Unix
+
+For Windows, ithreads allocates memory for each thread from a separate pool,
+which it discards at thread exit. It also checks that memory is free()d to
+the correct pool. Neither check is done on Unix, so code developed there won't
+be subject to such strictures, so can harbour bugs that only show up when the
+code reaches Windows.
+
+It would be good to be able to optionally emulate the Window pool system on
+Unix, to let developers who only have access to Unix, or want to use
+Unix-specific debugging tools, check for these problems. To do this would
+involve figuring out how the C<PerlMem_*> macros wrap C<malloc()> access, and
+providing a layer that records/checks the identity of the thread making the
+call, and recording all the memory allocated by each thread via this API so
+that it can be summarily free()d at thread exit. One implementation idea
+would be to increase the size of allocation, and store the C<my_perl> pointer
+(to identify the thread) at the start, along with pointers to make a linked
+list of blocks for this thread. To avoid alignment problems it would be
+necessary to do something like
+
+  union memory_header_padded {
+    struct memory_header {
+      void *thread_id;   /* For my_perl */
+      void *next;        /* Pointer to next block for this thread */
+    } data;
+    long double padding; /* whatever type has maximal alignment constraint */
+  };
+
+
+although C<long double> might not be the only type to add to the padding
+union.