Dr. Dobb's Journal - December 2007 - (Page 52)

d12gran_p5ma 10/12/07 10:27 AM Page 52 Core Technology TRANSACTIONAL PROGRAMMING continued from page 50 atomic::value name = "bill"; { atomic::transaction t1; name = "tom"; assert(*name == "tom"); { atomic::transaction t2; name = "fred"; assert(*name == "fred"); t2.commit(); } assert(*name == "fred"); // Committed by t2 } assert(*name == "bill"); // Rolled back by t1 The stored object is const, so that it cannot be accidentally modified in a way that cannot be rolled back by a transaction. Previous values are not destroyed until the end of the transaction, in case they need to be reincarnated. Transactional Pointers The Atomic Library provides shared pointers and weak pointers that are similar to the TR1 smart pointers (www.open-std.org/jtc1/ sc22/wg21/docs/papers/2005/n1745.pdf ). These pointers keep a counter of the number of pointers to the object. When the count reaches zero, the object can be deleted. These pointers do not destroy the pointee object until the end of the transaction in case the pointer needs to be rolled back, but the reference count (q.expired(), for example) behaves as if the object is destroyed. For instance: atomic::shared_ptr p(new int(1)); atomic::weak_ptr q(p); { atomic::transaction tr; p.reset(new int(2)); assert(q.expired()); assert(*p == 2); } assert(*p == 1); // Rolled back by tr assert(!q.expired()); // Rolled back by tr PC Presents Bug of the Month #1402 l st ge y oo d. on sl e t kin e l uou ar an Th n tw m nti of . . co sed s of . ti ry ver to ad e his th in -lint 8.0 for C/C++ #include class NorthPole { public: int Elves; double Toys; double Children; int Reindeer; static const int toysPerElf = 10000; static const int toysPerReindeer = 15000; NorthPole( double children ) { Santa is gearing up Toys = Children * 2; for this year's Elves = (int) (Toys / toysPerElf); Christmas Reindeer = (int) (Toys / toysPerReindeer); production. But his Children = children; new program is } }; showing unusually int main() small values. { What's going wrong? NorthPole np( 3e9 ); Visit our web site at printf( "Elves = %d, Toys = %g, Reindeer = %d\n", www.gimpel.com np.Elves, np.Toys, np.Reindeer ); return 0; } PC-lint for C/C++ will catch this and many other bugs. It will analyze a mixed suite of C and C++ modules to uncover bugs, glitches, quirks and inconsistencies. Not your Grandpa’s lint: PC-lint has introduced several spectacular and revolutionary innovations in the art of static program analysis. Taking clues from initializers, assignments, and conditionals, variable and member values are tracked, enabling reports on potential uses of null pointers and out-of-bounds subscripts. New with Version 8: Interfunction value tracking – Actual argument values are used to initialize parameters; return values are computed; a multipass operation (you control the number of passes) allows you to plumb the depths of function behavior to arbitrary levels. Plus Our Traditional C/C++ Warnings: Uninitialized variables, inherited non-virtual destructors, strong type mismatches,ill-formed macros, inadvertent name-hiding, suspicious expressions, etc., etc. Full Language Support for ANSI/ISO C and C++. If compatibility with std::tr1::shared_ptr is required, then a suitable approach would be atomic::value<std::tr1::shared_ptr >. Implementation The implementation of the Atomic Library is based around a central stack—a transaction stack—that logs each operation. Whenever an atomic container is modified, it pushes a record of the operation onto the stack. Each operation is recorded in the struct: struct Transaction { atomic::container* container; object_pointer node; enum { insertion, deletion } event; }; PC-lint for C/C++ Numerous compilers/ libraries supported. Runs on Windows, MS-DOS, and OS/2. $239 FlexeLint for C/C++ The same great product for other operating systems. Runs on all UNIX systems, VMS, mainframes, etc. Distributed in shrouded C source form. Call for pricing. 30 Day Money Back Guarantee G i m p e l S o f t wa r e Serving the C/C++ Community for 22 Years. When a transaction is entered, the constructor of atomic::transaction stores the initial size of the transaction stack. When a transaction exits, the destructor of atomic::transaction can roll back all operations (in reverse order) to the initial size of the transaction stack. The transaction::commit() method sets a flag in the transaction telling it not to roll back. There are just two types of atomic operations—insert and delete. Other operations can be composed of insertions or deletions. All atomic containers derive from atomic::container: class container { public: CALL TODAY (610) 584-4261 Or FAX (610) 584-4266 www.gimpel.com PC-lint and FlexeLint are trademarks of Gimpel Software 52 Dr. Dobb’s Journal l www.ddj.com l December 2007 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1745.pdf http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1745.pdf http://www.gimpel.com http://www.gimpel.com http://www.gimpel.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - December 2007

Dr. Dobb's Journal - December 2007 Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook Computer Books: Reading Between the Lines Conversations Query Anything with SQLite XQuery Web Maps with the Google Map API OpenALM and Its Manifesto Transactional Programming Effective Concurrency The Agile Edge Swaine’s Flames

Dr. Dobb's Journal - December 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.