86aa28644c
Correctly set errno on failure and improve the related test. Previously the malloc test would emit an error message but not abort if the errno was not as expected on failure. This was because the return in the null == true case prevented the check for failed == true at the end of check_result from being reached. To resolve this just abort immediately as in the null case. Also add tests of allocations that are expected to fail for calloc and malloc. To make the tests pass we need to set errno in several places, making sure to keep this off the fast path. We must also take care not to attempt to zero nullptr in case of calloc failure. See microsoft/snmalloc#461 and microsoft/snmalloc#463.
snmalloc
snmalloc is a high-performance allocator.
snmalloc can be used directly in a project as a header-only C++ library,
it can be LD_PRELOADed on Elf platforms (e.g. Linux, BSD),
and there is a crate to use it from Rust.
Its key design features are:
- Memory that is freed by the same thread that allocated it does not require any synchronising operations.
- Freeing memory in a different thread to initially allocated it, does not take any locks and instead uses a novel message passing scheme to return the memory to the original allocator, where it is recycled. This enables 1000s of remote deallocations to be performed with only a single atomic operation enabling great scaling with core count.
- The allocator uses large ranges of pages to reduce the amount of meta-data required.
- The fast paths are highly optimised with just two branches on the fast path for malloc (On Linux compiled with Clang).
- The platform dependencies are abstracted away to enable porting to other platforms.
snmalloc's design is particular well suited to the following two difficult scenarios that can be problematic for other allocators:
- Allocations on one thread are freed by a different thread
- Deallocations occur in large batches
Both of these can cause massive reductions in performance of other allocators, but do not for snmalloc.
Comprehensive details about snmalloc's design can be found in the accompanying paper, and differences between the paper and the current implementation are described here. Since writing the paper, the performance of snmalloc has improved considerably.
Further documentation
Contributing
This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.
When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.
This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.