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Groups > comp.programming.threads > #277
| From | Anthony Williams <anthony.ajw@gmail.com> |
|---|---|
| Newsgroups | comp.programming.threads |
| Subject | Re: questions about memory_order_seq_cst fence |
| References | <43eb372b-6517-4914-b647-860f1f7136ba@k15g2000pri.googlegroups.com> |
| Date | 2011-06-14 23:05 +0100 |
| Message-ID | <87tybsm5kq.fsf@justsoftwaresolutions.co.uk> (permalink) |
| Organization | CNNTP |
Masakuni Oishi <yamasa@bsdhouse.org> writes: > /*** code 1 ***/ > // Initially > atomic<int> x(0), y(0); > > // Thread 1: > y.store(1, memory_order_release); > atomic_thread_fence(memory_order_seq_cst); > r1 = x.load(memory_order_acquire); > > // Thread 2: > x.store(1, memory_order_release); > > // Thread 3: > r2 = x.load(memory_order_acquire); > atomic_thread_fence(memory_order_seq_cst); > r3 = y.load(memory_order_acquire); > /***************/ > > In the above code, is r1 == 0 && r2 == 1 && r3 == 0 possible? > I think it should be prohibited, but I couldn't make sure that > from the C++0x FDIS. Premise 1: r3 == 0. Since the only store to y is the store of 1 by thread 1, r3 == 0 implies that the load from y on thread 3 is reading the initial value of y. 29.3p6 of N3290 says: "For atomic operations A and B on an atomic object M, where A modifies M and B takes its value, if there are memory_order_seq_cst fences X and Y such that A is sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes either the effects of A or a later modification of M in its modification order." If the fence in thread 1 precedes the fence in thread 3 in S, then the read at r3 must therefore see the value written by the store in thread 1. Consequently, the fence in thread 3 must precede the fence in thread 1 in S. Premise 2: r2 == 1. The load of x in thread 3 reading 1 implies it has read the value of the store to x from thread 2. We already know that the fence in thread 3 precedes the fence in thread 1 in S. 29.3p7 of N3290 says: "For atomic operations A and B on an atomic object M, if there are memory_order_seq_cst fences X and Y such that A is sequenced before X, Y is sequenced before B, and X precedes Y in S, then B occurs later than A in the modification order of M." In our case, the fence in thread 3 occurs before the fence in thread 1 in S. The fence in thread 3 is thus X, the fence in thread 1 Y, the read from x in thread 3 is A and the read from x in thread 1 is B. Thus the read of x in thread 1 must occur later in the modification order of x than the read in thread 3. Since the read in thread 3 is of the last store to x (1), the read in thread 1 must also read that value, and r1 == 1. Therefore r1==0, r2 == 1 and r3 == 0 is not possible. > So, my questions are: > For code 1, is r1 == 0 && r2 == 1 && r3 == 0 allowed in the C++0x > FDIS? No. Anthony -- Author of C++ Concurrency in Action http://www.stdthread.co.uk/book/ just::thread C++0x thread library http://www.stdthread.co.uk Just Software Solutions Ltd http://www.justsoftwaresolutions.co.uk 15 Carrallack Mews, St Just, Cornwall, TR19 7UL, UK. Company No. 5478976
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questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-13 09:40 -0700
Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-13 22:39 +0200
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-14 08:27 -0700
Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-16 00:21 +0200
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 15:48 -0700
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-16 05:03 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 08:35 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 12:05 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 11:19 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 13:57 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:51 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 16:53 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:17 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 17:37 +0200
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:47 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:54 +0100
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 09:01 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 17:07 +0100
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 13:59 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-16 14:32 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-17 08:03 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-17 16:19 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-17 15:40 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-30 14:26 +0200
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-17 15:24 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 03:49 -0700
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-18 14:40 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 15:46 -0700
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-18 20:27 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 21:31 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 21:37 -0700
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-20 15:45 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 20:05 -0700
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 14:06 +0200
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 18:32 +0200
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 15:42 -0700
Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-07-10 19:47 +0200
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:51 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 17:23 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 18:49 +0200
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:51 -0700
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 17:25 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:56 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 14:28 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 09:54 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-20 15:39 +0200
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-22 13:24 +0200
Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-16 14:39 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:55 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 12:03 +0200
Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-07-10 19:10 +0200
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-13 16:00 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-13 23:31 -0700
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-14 08:32 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-14 23:05 +0100
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-14 16:44 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-15 08:34 +0100
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-15 02:11 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 15:58 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 08:26 +0100
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-16 05:05 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:11 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 15:42 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 09:27 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-20 15:30 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 15:00 +0100
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 14:54 +0200
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 18:37 +0200
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 15:59 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-22 09:01 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 15:41 +0100
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-20 23:24 -0700
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 10:46 -0700
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 11:19 -0700
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 11:57 -0700
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-27 14:05 +0200
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-29 16:14 -0700
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-24 01:42 -0700
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-27 13:24 +0200
Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-07-01 02:25 -0700
Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-07-01 12:48 +0200
Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-15 01:53 -0700
Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 02:57 -0700
Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-15 02:06 -0700
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