Thank you Pavel for your comments, I would like to comment on some things
1. The HTML documentation does't allow to change font in browser. 2. End of document can be marked so it doesn't look like cut in half during transmission. 3. docs 3.2:
Sorry for errors and bad html. It was generated from MS Word so I will try to rewrite it using plan html. I'll change that shortly.
4. Example in 3.2: the "alignement" parameter in segment.create() isn't found in code.
I can't find the error you mention, I've just downloaded the zip file and 3.2 does not have any example. In 4.2 segment.create is missing a ",".
5. Example in 4.2: segment.named_new<MyType> ("MyType instance", /*name of the object*/ 10 /*number of elements*/, false /*if previously present, return error*/, 0 /*ctor first argument*/, 0 /*ctor second argument*/);
a.It returns false. Exceptions are used only to indicate memory errors throwing bad_alloc. You are right there is info missing here. I will add more documentation in examples. b.If you find this approach more useful, I have no problem. I really don't like the boolean parameter, but I wanted to have a "find or create" functionality. If you like a find_or_named_new<>() additional function to indicate that approach I find it more clear than with a boolean parameters. c.The syntax you propose is better, no doubt. I don't have experience with it so to implement this I suppose named_new<> should return an proxy object with overloaded operator()() functions. Is that right? If you want to help me I'm open. If boosters prefer throwing exceptions instead or returning false no problem here. A problem I see is that my interface allows creating an array like new[]. Do you consider this necessary? You prefer a different function? Maybe the proxy object should have an operator[] that can be used to specify array allocation?
std::pair< MyType *, std::size_t> res = segment.find_named_new< MyType > ("MyType instance"); Why do I need the "size"? Doesn't a type have always the same size regardless?
Size contains the number of elements in case you allocate an array. with segment.named_new<MyType> ("MyType instance", /*name of the object*/ 10 /*number of elements*/, ... you allocate an array of 10 elements. so it will return 10.
6. Could you use namespace shmem_detail or so instead of "detal" to avoid possible clashes? No problem. I've seen detail namespace in some projects so I thought it was not a problem. detail namespace is inside boost::shmem namespace so it wouldn't be necessary. You find it necessary even if detail namespace is really boost::shmem::detail?
7. exceptions.hpp: a) file name should be shmem_exceptions.hpp or so
No problem
b) does it make sense to have common base for both exceptions there?
My exception handling experience is null, so I based all in thread exception examples, where lock_error inherits from thread_exception. No problem changing this is you find it necessary.
8. offset_ptr.hpp: full_offset_ptr class a) using char as de-facto bool class has usually no practical advantage and may be actually slowe.
No problem. You are right, with all platforms using 4 byte alignment bool and char use the same space and it can be slower I suppose due to mask operations.
b) The flag could be eliminated completely. If m_offset == 0 it is NULL pointer and no data allocated in shmem will starts on the beginning. This would also eliminate need for min_offset_ptr.
The offset indicates the distance between the pointee and the this pointer of offset_ptr, so m_offset == 0 indicates a pointer pointing to itself and this is quite common in STL containers when empty, since next pointer in the end node points to end node, resulting in a m_offset = 0. Obviously this is different from a null pointer. If I change the meaning of m_offset to offset from the beginning of the segment I need the base address stored somewhere (and the base address is different in each process), so that I can convert from offset_ptr<A> to A* using get() or the constructor. Using my approach I can convert between A* and offset_ptr<A> without any additional data. Obviously, your approach is more performance friendly since m_offset does not need to be changed with each assignment and constructor. If boost people find the additional member as a waste comparing to A* <-> offset_ptr<A> conversions I would change it but I find my approach quite useful, since I don't want to deal with base addresses stored somewhere for each process when building a offset_ptr.
c) swap() could be added and other operators.
Ok. I will add it. Which other operator you miss?
9. Maybe the protection of mutext from shared ptr lib could be worked around
10. The example in 4.3 uses very dirty C-like approach with casts. Cannot it be rewritten in C++ way with overloaded new? If you refer to (list_node*)segment.allocate(...) line, segment in this case is a low-level void* returning function. If you prefer an allocate<Type> approach, I don't have any problem, but remember that
I don't understand your point. Could you give me an example please? this segment object is of type shmem_alloc which allocs raw memory, something like when writing your own void* operator new(size_t size) for a class. If you have I workaround in mind, please let me know.
11. Some source files use Unix line ends, some DOS line ends. Just bit strange. It's because I've tested and changed things in both windows and linux. I'll try to convert all to a common line feed.
12. The simple algorithm to find fitting memory block may not be adequate for high-performance apps (who are most likely to use shared memory).
You are right. The default algorithm is space-friendly, which I thought it was more important than performance for fixed size segments. You can write your own algorithm and use it since shmem_alloc is a typedef of basic_shmem_alloc<default_algo>. If you prefer another algo like segregated lists, I can try to write it, so that the user can choose the allocation algorithm. I've written the pooled allocator due to default algorithm slowness.
13. Can be be possible to identify named objects with something else than C string? Say wchar_t* or numeral or other templated type?
Well, I've chosen a c string as an universal name, but other types could be used. Do you think that the key type should be templatized? I think that an integer key can speed up a lot searches but I have to think about which classes should be templatized. When storing other type of strings (for example std::string, I would need to build an allocator for strings in shared memory but also a std::string since it's probable that current STL won't work with Shemem STL allocator). The key meaning would be different since right now, I copy the string to shared memory but with configurable key type things are more complicated.
14. What I would like to see: a) avoiding shmem specific containers/mutexes/etc as much as possible.
I think you can't avoid mutexes if you want to guarantee atomic memory allocation, since I have no skills to write a lock-free memory allocator. Regarding to containers, it was no my intention to write them, but I needed some of them to store name-buffer mappings and a node container to test the pooled allocator in several systems. For now, I have only succeed using shmem STL allocators in a modified Dinkum STL. STLport and libstc++ use suppose allocator::pointer to be a raw pointer, so I can't use STL containers. I've chosen internal containers to be public because I find them very useful, but if this is not accepted they can be used only for internal uses and removed from documentation. Regarding mutexes and etc... can you be more explicit? I propose mutexes to be general. If boost want to implement process-shared mutexes in other way, say in another library, I would use them, but for the moment, this is all that I have.
b) ability to "equalize" shared memory features
I would need some help in this because my operating system knowledge is very limited. Mimic-ing UNIX way in windows can be very difficult, I think, unless you use a mapped file. I would need some serious help here.
c) support for inheritance in shmem using object factories, e.g. like one in Classloader http://s11n.net/papers/classloading_cpp.html
I'll check it. Thanks for the url.
d) support for "transactions": I would like to
My knowledge in transaction world is null so I can't help you with that. I suppose that a shared memory condition variable should be very interesting to notify events to other processes, but I'm afraid this is a work for more skilled programmers than me (people from boost::threads, perhaps?). As far as I know in windows is difficult to implement a shared memory condition variable, pthreads-win32 does no support it and I don't know how cygwin solves this. Thank you again for all your comments. I would like to make some changes you've suggested, so I will wait your response regarding open issues and comments from other boosters before doing any change. Regards, Ion