Author: Armin Rigo <[email protected]>
Branch:
Changeset: r417:6bde91a8f3f9
Date: 2013-07-19 11:20 +0200
http://bitbucket.org/pypy/stmgc/changeset/6bde91a8f3f9/
Log: Add comments about the barrier placement
diff --git a/c4/stmgc.h b/c4/stmgc.h
--- a/c4/stmgc.h
+++ b/c4/stmgc.h
@@ -54,11 +54,19 @@
int stm_enter_callback_call(void);
void stm_leave_callback_call(int);
-/* read/write barriers (the most general versions only for now) */
-#if 0 // (optimized version below)
-gcptr stm_read_barrier(gcptr);
-gcptr stm_write_barrier(gcptr);
-#endif
+/* read/write barriers (the most general versions only for now).
+
+ - the read barrier must be applied before reading from an object.
+ the result is valid as long as we're in the same transaction,
+ and stm_write_barrier() is not called on the same object.
+
+ - the write barrier must be applied before writing to an object.
+ the result is valid for a shorter period of time: we have to
+ do stm_write_barrier() again if we ended the transaction, or
+ if we did a potential collection (e.g. stm_allocate()).
+*/
+static inline gcptr stm_read_barrier(gcptr);
+static inline gcptr stm_write_barrier(gcptr);
/* start a new transaction, calls callback(), and when it returns
finish that transaction. callback() is called with the 'arg'
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