C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Using garbage collection in C++          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Pedro Miguel Carvalho Guest Posted: Sun Sep 26, 2004 5:34 pm    Post subject: Using garbage collection in C++ Greetings. I'm creating a project that as a intricate relation between object kind of like a set where each object in the set can be connect to a subset of object of the set and objects not in the set can connect to objects in the set. Every object inherits a interface to allow for a mark and sweep garbage collector (GC) and my implementation works correctly and efficiently but only in a single thread. How can I garbage collect in a multi-thread program? With my garbage collector all threads have to stop what they are doing but in a coherent state before the garbage collector can do it's job. I could signal all thread that a garbage collection is needed and wait for all the treads to be ready then execute the garbage collection but it would mean that some thread would have to wait (possibly a long time) before all thread are ready and the garbage collector can start. I have also tried the Hans-Boehm conservative GC (HBGC) in single-thread (both the interface for my GC and my GC are off) and it worked correctly. It takes 5-8% more CPU time, very acceptable, but it uses 79-96% more memory and that is not acceptable (measured max and mix CPU and memory used in 100 test runs). The test runs uses less CPU time and memory than a full run. In fact in a full run the HBGC would use virtual memory in my 512 MB development system and that as you can imagine is a big no-no. Is this excess memory use normal or am I doing something wrong? Comments are very much appreciated. Thanks, Pedro Carvalho Back to top Dave Rahardja Guest Posted: Sun Sep 26, 2004 8:49 pm    Post subject: Re: Using garbage collection in C++ Pedro Miguel Carvalho wrote: Quote: How can I garbage collect in a multi-thread program? This is off-topic for C++. Try looking for help in an algorithms newsgroup, or do a search on the subject of thread synchronization. Hint: interlock the access to your "ready to garbage collect" member variable. There's no reason why all threads have to stop when you garbage collect. Back to top Derrick Coetzee Guest Posted: Sun Sep 26, 2004 11:13 pm    Post subject: Re: Using garbage collection in C++ Pedro Miguel Carvalho wrote: Quote: I have also tried the Hans-Boehm conservative GC (HBGC) in single-thread (both the interface for my GC and my GC are off) and it worked correctly. It takes 5-8% more CPU time, very acceptable, but it uses 79-96% more memory and that is not acceptable (measured max and mix CPU and memory used in 100 test runs). The test runs uses less CPU time and memory than a full run. In fact in a full run the HBGC would use virtual memory in my 512 MB development system and that as you can imagine is a big no-no. Hans-Boehm should work fine. If you want to avoid the extra storage it requires between collection cycles, try adding a reference-counting mechanism to some of your acyclic structures (for example, by using smart pointers to refer to them). Then there will be less garbage building up between cycles. You may also be able to make it collect more often, or when usage reaches a certain level. -- Derrick Coetzee I grant this newsgroup posting into the public domain. I disclaim all express or implied warranty and all liability. I am not a professional. Back to top Pedro Miguel Carvalho Guest Posted: Mon Sep 27, 2004 10:20 am    Post subject: Re: Using garbage collection in C++ "Derrick Coetzee" <dcnews (AT) moonflare (DOT) com> wrote Quote: Pedro Miguel Carvalho wrote: I have also tried the Hans-Boehm conservative GC (HBGC) in single-thread (both the interface for my GC and my GC are off) and it worked correctly. It takes 5-8% more CPU time, very acceptable, but it uses 79-96% more memory and that is not acceptable (measured max and mix CPU and memory used in 100 test runs). The test runs uses less CPU time and memory than a full run. In fact in a full run the HBGC would use virtual memory in my 512 MB development system and that as you can imagine is a big no-no. Hans-Boehm should work fine. If you want to avoid the extra storage it requires between collection cycles, try adding a reference-counting mechanism to some of your acyclic structures (for example, by using smart pointers to refer to them). Then there will be less garbage building up between cycles. You may also be able to make it collect more often, or when usage reaches a certain level. -- Derrick Coetzee One of my implementations uses reference-counting smart-pointers for some objects but for the data set I use a mark-sweep GC. I'm trying to use a GC because of the extensive cycles that form on my data set so basic reference-counting will not be a solution. If I make the Hans-Boehm collector work more then it's use of the CPU also increases. Thanks, Pedro Carvalho Back to top Pedro Miguel Carvalho Guest Posted: Mon Sep 27, 2004 10:36 am    Post subject: Re: Using garbage collection in C++ "Dave Rahardja" <ask (AT) me (DOT) com> wrote Quote: Pedro Miguel Carvalho wrote: How can I garbage collect in a multi-thread program? This is off-topic for C++. Try looking for help in an algorithms newsgroup, or do a search on the subject of thread synchronization. Sorry about that. I looked for an appropriate newsgroup. I found various *.graphics.algorithms, not appropriate, and various *.comp.algorithms, none in english. I will try in comp.programming.threads, not exactly what I need, another off-topic . Quote: Hint: interlock the access to your "ready to garbage collect" member variable. There's no reason why all threads have to stop when you garbage collect. To garbage collect the data set I have to be certain that I see a consistent state, other GC use write/read barriers for this. 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