Author: Armin Rigo <ar...@tunes.org>
Branch: c7-refactor
Changeset: r767:94ed263ba9d2
Date: 2014-02-18 15:42 +0100
http://bitbucket.org/pypy/stmgc/changeset/94ed263ba9d2/
Log: Comments about v_nursery_section_end
diff --git a/c7/stm/nursery.h b/c7/stm/nursery.h
--- a/c7/stm/nursery.h
+++ b/c7/stm/nursery.h
@@ -3,5 +3,30 @@
#define NSE_SIGNAL 1
#define NSE_SIGNAL_DONE 2
+/* Rules for 'v_nursery_section_end':
+
+ - Its main purpose is to be read by the owning thread in stm_allocate().
+
+ - The owning thread can change its value without acquiring the mutex,
+ but it must do so carefully, with a compare_and_swap.
+
+ - If a different thread has the mutex, it can force the field to the
+ value NSE_SIGNAL or NSE_SIGNAL_DONE with a regular write. This should
+ not be hidden by the compare_and_swap done by the owning thread:
+ even if it occurs just before or just after a compare_and_swap,
+ the end result is that the special value NSE_SIGNAL(_DONE) is still
+ in the field.
+
+ - When the owning thread sees NSE_SIGNAL, it must signal and wait until
+ the other thread restores the value to NSE_SIGNAL_DONE. When the
+ owning thread sees NSE_SIGNAL_DONE, it can replace it, again with
+ compare_and_swap, with the real value.
+
+ - This should in theory be a volatile field, because it can be read
+ from stm_allocate() while at the same time being changed to the value
+ NSE_SIGNAL by another thread. In practice, making it volatile has
+ probably just a small negative impact on performance for no good reason.
+*/
+
static void align_nursery_at_transaction_start(void);
static void restore_nursery_section_end(uintptr_t prev_value);
diff --git a/c7/stmgc.h b/c7/stmgc.h
--- a/c7/stmgc.h
+++ b/c7/stmgc.h
@@ -62,7 +62,7 @@
int segment_num;
char *segment_base;
stm_char *nursery_current;
- volatile uintptr_t v_nursery_section_end; /* see nursery.h */
+ uintptr_t v_nursery_section_end; /* see nursery.h */
struct stm_thread_local_s *running_thread;
stm_jmpbuf_t *jmpbuf_ptr;
};
_______________________________________________
pypy-commit mailing list
pypy-commit@python.org
https://mail.python.org/mailman/listinfo/pypy-commit
