> From: Mark Thomas [mailto:ma...@apache.org] > Subject: Re: RV-Predict bugs
> Putting it into my own words to check my understanding: > - The two reads in T2 may be re-ordered because, in T2, there is nothing > that requires a happens-before relationship between the two reads Depends on what was really meant by the ??? notation. If it were another reference to st_200, then the example ignores the potential write to st_200. > - If T2 was executing in isolation the order of the reads wouldn't > matter Correct, assuming there is no write in T2's control flow. > - However, T1 is writing. > So if the writes I'll assume you meant "reads" there. > in T2 are re-ordered and the write from T1 takes place between them the T2 > read for the line 'st_200 == null' could return a non-null value for st_200 > (the value after the write from T1) while the read for the line 'return > st_200;' could return null (the value from before the write in T1). No - that would violate program order (intra-thread semantics). The compiler cannot legally move the read for "return st_200" to a point before the potential write to st_200. The CPU can speculatively read for the return value, but must discard such speculation if a write were to occur (or use store forwarding to update the read). - Chuck THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY MATERIAL and is thus for use only by the intended recipient. If you received this in error, please contact the sender and delete the e-mail and its attachments from all computers. --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@tomcat.apache.org For additional commands, e-mail: dev-h...@tomcat.apache.org
