[Chicken-users] Egg example
Hi all, I've decided to try my hand a writing an egg. I'm one of those people who learn best by example. But when I try to download the mpeg3 example fromk SVN I'm told the URL does not exist. Am I doing something wrong or is the tutorial wrong?I have not yet started writing an egg - I just want to see an example of how it's done. Bill ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] Egg example
* bill ramsa...@comcast.net [090721 13:43]: Hi all, I've decided to try my hand a writing an egg. I'm one of those people who learn best by example. But when I try to download the mpeg3 example fromk SVN I'm told the URL does not exist. Am I doing something wrong or is the tutorial wrong?I have not yet started writing an egg - I just want to see an example of how it's done. Maybe you are using an URL from outdated documentation? The url that works for me is: https://galinha.ucpel.tche.br/svn/chicken-eggs/release/3/mpeg3 Replace 3 by 4 if you want the eggs for chicken4. The username is anonymous, the password is empty. Cheers, Christian ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] Egg example
Christian, I tried release 4 and it did not work. I then tried 3 and it did. I'm fine now, but there may be a problem with release 4. Thanks for the help. Bill Christian Kellermann wrote: * bill ramsa...@comcast.net [090721 13:43]: Hi all, I've decided to try my hand a writing an egg. I'm one of those people who learn best by example. But when I try to download the mpeg3 example fromk SVN I'm told the URL does not exist. Am I doing something wrong or is the tutorial wrong?I have not yet started writing an egg - I just want to see an example of how it's done. Maybe you are using an URL from outdated documentation? The url that works for me is: https://galinha.ucpel.tche.br/svn/chicken-eggs/release/3/mpeg3 Replace 3 by 4 if you want the eggs for chicken4. The username is anonymous, the password is empty. Cheers, Christian ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
[Chicken-users] FFI and stack use
I have an FFI function, and it will be allocating some significant stack space. (It calls the Linux syscall epoll_wait, with a significant stack-allocated array, and then wants to cons the results into a list.) So this raises a question. Scheme functions get compiled into code that carefully checks stack bounds before allocating, and bangs off to the garbage collector if necessary. The FFI doesn't do this. So I'm assuming that in fact, I have the full C stack available, and can just go ahead and use it. When I invoke the return continuation, it will go just fine, and presumably if I've exceeded the Chicken stack size, it will just trigger a gc and proceed happily as before. Am I right? Thomas ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] FFI and stack use
Thomas Bushnell BSG scripsit: So this raises a question. Scheme functions get compiled into code that carefully checks stack bounds before allocating, and bangs off to the garbage collector if necessary. The FFI doesn't do this. So I'm assuming that in fact, I have the full C stack available, and can just go ahead and use it. When I invoke the return continuation, it will go just fine, and presumably if I've exceeded the Chicken stack size, it will just trigger a gc and proceed happily as before. In fact, it's unpredictable how much C stack you have, because each compiled Scheme function invokes its successor, leaving garbage return addresses, saved registers, etc. on the C stack. So just before calling a function that allocates lots of C stack, call (gc #f) to force a minor GC. Alternatively, use the -nursery switch at compile time or the -:s switch at run time to force a large stack. -- John Cowanco...@ccil.orghttp://ccil.org/~cowan Heckler: Go on, Al, tell 'em all you know. It won't take long. Al Smith: I'll tell 'em all we *both* know. It won't take any longer. ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] FFI and stack use
Thomas Bushnell BSG t...@becket.net writes: I have an FFI function, and it will be allocating some significant stack space. (It calls the Linux syscall epoll_wait, with a significant stack-allocated array, and then wants to cons the results into a list.) So this raises a question. Scheme functions get compiled into code that carefully checks stack bounds before allocating, and bangs off to the garbage collector if necessary. The FFI doesn't do this. So I'm assuming that in fact, I have the full C stack available, and can just go ahead and use it. When I invoke the return continuation, it will go just fine, and presumably if I've exceeded the Chicken stack size, it will just trigger a gc and proceed happily as before. Am I right? Thomas In C, when you make a mess, you must clean it up yourself. For this reason, I treat all my FFI calls like toxic waste, and wrap them in (let ... ) containers which allocate everything I need for the FFI call. I get pointers using (location ...) and call the C function. After the FFI call returns, the closing ) of the let establishes scope and the GC can do whatever it wants after that. It has never eaten my stuff before the ), so this seems to work. The last line before the ) is a call to cons or append or list with whatever I need from my let. This is how I write wrappers. It Works For Me (TM). For event-driven programs with external C contexts and data structures, you need an event loop which calls (collect-c-garbage context) which checks your program state and calls free() when needed. You need to write (collect-c-garbage) yourself, and fill it with conditionals and calls to free(). For programs with I/O structures or AI genetic algorithms or whatever, you can probably come up with reasonable conditionals for when you need or don't need something anymore. Read through the lolevel unit docs in the manual about tools you can use for this. With persistent data out in C-land, an event loop with a custom GC is excellent form I think. Within the loop, you pass pointers around and use them and then do a check at the end of each iteration. Those are two easy ways of making C behave. They add overhead. They are simple and difficult to screw up. Then, there is the incredibly scary alternative which involves sprinkling your functions with FFI calls to alloc() and free() and then trying to map out the state space and all possible transitions and drawing epic flow diagrams to try and match up calls to alloc() and free(). This is not a good idea because life is short, and even if you spend 100 hours doing this, you will still screw it up. I promise. Lastly, there is the overwhelmingly popular option of doing the above, but not worrying about matching up calls to alloc() and free(). If you want an example of this ... well I'll stop before I become really offensive. Let me just state that *some* languages lack GC, and that *some* software in those languages use lots of memory. I am not kidding. In 2009, this is still true. I haven't looked at the chicken source code, but I don't really want to, because then I will think I am smart and will use GC tricks that are not portable to other implementations. Or worse, I might learn that my let statements are not safe from the GC and that I should use object-evict to be totally safe. So far, the GC has not harmed me and has respected the closing ) of the let before moving anything. -Rafael ___ Chicken-users mailing list Chicken-users@nongnu.org http://lists.nongnu.org/mailman/listinfo/chicken-users
