On 26 February 2012 00:55, Walter Bright <newshound2@digitalmars.com> wrote:On 2/25/2012 2:08 PM, Paulo Pinto wrote:
Most straight up GC vs malloc/free benchmarks miss something crucial. A GC allows one to do substantially *fewer* allocations. It's a lot faster to not allocate than to allocate.Most standard compiler malloc()/free() implementations are actually slower than
most advanced GC algorithms.
Do you really think that's true? Are there any statistics to support that?I'm extremely sceptical of this claim.I would have surely thought using a GC leads to a significant increase in allocations for a few reasons:It's easy to allocate, ie, nothing to discourage youIt's easy to clean up - you don't have to worry about cleanup problems, makes it simpler to use in many situationsDynamic arrays are easy - many C++ users will avoid dynamic arrays because the explicit allocation/clean up implies complexity, one will always use the stack, or a fixed array where they can get away with itSlicing, concatenation, etc performs bucket loads of implicit GC allocations
Strings... - C coders who reject the stl will almost always have a separate string heap with very particular allocation patterns, and almost always refcountedPhobos/druntine allocate liberally - the CRT almost never allocatesThis is my single biggest fear in D. I have explicit control within my own code, but I wonder if many D libraries will be sloppy and over-allocate all over the place, and be generally unusable in many applications.If D is another language like C where the majority of libraries (including the standard libraries I fear) are unusable in various contexts, then that kinda defeats the purpose. D's module system is one of its biggest selling points.I think there should be strict phobos allocation policies, and ideally, druntime should NEVER allocate if it can help it.
Consider C strings. You need to keep track of ownership of it. That often means creating extra copies, rather than sharing a single copy.Rubbish, strings are almost always either refcounted or on the stack for dynamic strings, or have fixed memory allocated within structures. I don't think I've ever seen someone duplicating strings into separate allocations liberally.
Enter C++'s shared_ptr. But that works by, for each object, allocating a *second* chunk of memory to hold the reference count. Right off the bat, you've got twice as many allocations & frees with shared_ptr than a GC would have.
Who actually uses shared_ptr? Talking about the stl is misleading... an overwhelming number of C/C++ programmers avoid the stl like the plague (for these exact reasons). Performance oriented programmers rarely use STL out of the box, and that's what we're talking about here right? If you're not performance oriented, then who cares about the GC either?