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a parallelized, amortized-constant time allocator for objects smaller than a hardware page.
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README.markdown

ramalloc (alpha)

ramalloc is a parallelized, amortized-constant time allocator for objects smaller than a hardware page. it exhibits deterministic performance characteristics, which is necessary for soft real-time applications. it also reduces memory fragmentation, which is important for long-running processes. ramalloc is designed for game and interpreter development but should be useful for other applications as well. ramalloc is also parallelized; there is no global resource that requires serialized access.

if you choose to integrate ramalloc into your application, please read this entire document before starting. an improper integration is likely to leak an unacceptable amount of memory.

features

  • deterministic performance (amortized-constant time).
  • low fragmentation.
  • limited waste (a 4 byte object can have less than 1 byte of overhead).
  • coexists with a supplementary heap allocator.
  • query any valid base pointer to determine source allocator, if any.
  • returns unused memory to the system.
  • parallelized.

requirements

  • a C89 compiler (to-date, only MSVC 2010 and GCC 4.4.4 have been tested).
  • CMake.
  • trio, which is already included for you in the source distribution.
  • support for threads.
  • Windows or Linux, though other ports should require little effort.

license

ramalloc source code is provided under the New BSD License.

this means that you are free to use ramalloc for any purpose you see fit, as long as you give proper credit for my work.

you're not required to distribute source code if you use ramalloc. if you don't, you can satisfy the credit requirement by crediting me in the about box (in a GUI application), a usage message (in a command-line application), or in a credits list (in a game).

see the LICENSE file in the source distribution for more details.

history

ramalloc is based on an allocator i wrote for the MMORPG Horizons, before it was released in 2003. the intention its design was to reduce the allocation rate that the many interpreters imposed on the (global) heap allocator, while eliminating obstacles to parallelism.

ramalloc is named after a well known image macro.

usage

ramalloc diverges from traditional memory allocation semantics in order to better serve the needs of parallelism.

traditional allocators provide a two-operation interface: allocate and deallocate. ramalloc, in order to minimize competition for resources basically provides a three-operation interface: acquire, discard, and reclaim.

  • the acquire operation allocates memory and usually reclaims a small amount of discarded memory.

  • the discard operation informs the allocator that memory can be reclaimed. this is the only operation that used with memory allocated by a different thread.

  • the reclaim operation deallocates discarded memory.

these operations can easily be mapped onto a traditional allocate/deallocate interface, and are. the likelihood of asymmetrical allocation patterns, however, requires that each allocating thread service ramalloc with reclaim operations regularly (e.g. as part of the event loop).

ramalloc provides additional operations that are also useful:

  • a query operation tells whether a given address was acquired from ramalloc and the size, if indeed it was. queries do not crash the application if the provided address was acquired from some sort of allocator, making this operation useful for layering ramalloc on top of a supplementary allocator.

  • a flush operation reclaims memory more quickly than reclaim but at the expense of deterministic performance.

important considerations

ramalloc, unlike other allocators, will leak memory if you do not periodically service it with reclaim operations from each memory-producing thread. this might seem inconvenient but makes it possible to perform most operations without serializing threads.

other considerations exist that you should be aware of when integrating any custom allocator such as ramalloc.

should an error such as a buffer overrun occur, ramalloc would more likely corrupt memory than crash the process. this is because ramalloc does not use guard bytes or guard pages. therefore, i recommend that you reserve ramalloc for release builds or refrain from integrating ramalloc until you have thoroughly debugged your application. otherwise, you risk hiding bugs not yet discovered.

also, i do not recommend using ramalloc with a tool such as IBM Rational Purify, valgrind, or HeapAgent. these are fantastic tools but unless integrated though a tool-specific API, memory pooling strategies hide memory errors from these tools. i recommend that you prepare a specific build for use with these tools that uses only the default system allocator.

status

i consider ramalloc to be of alpha quality.

ramalloc is complete, however, and should be bug free. i am strict about error checking (and reporting) and there are numerous tests, each validating a different module in the library.

still, ramalloc has not yet been tested in a real application. once it has, and once i've worked through enough outstanding issues, i'll announce that the project has entered beta status.

known issues

  • ramalloc is poorly documented. this is my first priority, in the absence of unanticipated bugs.

  • i intend to clean up and refactor the code, so i cannot guarantee that the API will remain constant until the next major release (i.e. release 1).

  • ramalloc is not yet optimized. the allocator should be attractive nonetheless because it should not pause processing for an undesirable period of time to no matter how high your allocation rate is.

  • ramalloc requires threads that allocate to be running until they have no outstanding allocations remaining. this makes ramalloc incompatible with applications that create and destroy threads with any sort of frequency. please consider using a thread pool until i am able to address this issue.

  • ramalloc leaks memory stored in thread local storage. while sloppy, it is a small, finite quantity of memory that should be harmless if leaked.


README.markdown for ramalloc by michael lowell roberts.
copyright © 2011, michael lowell roberts.
all rights reserved.
licensed under the New BSD License.

fmrl

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