# jemalloc-sys - Rust bindings to the `jemalloc` C library
[![Travis-CI Status]][travis] [![Latest Version]][crates.io] [![docs]][docs.rs]
> Note: the Rust allocator API is implemented for `jemalloc` in the
> [`jemallocator`](https://crates.io/crates/jemallocator) crate.
## Documentation
* [Latest release (docs.rs)][docs.rs]
`jemalloc` is a general purpose memory allocator, its documentation
can be found here:
* [API documentation][jemalloc_docs]
* [Wiki][jemalloc_wiki] (design documents, presentations, profiling, debugging, tuning, ...)
[jemalloc_docs]: http://jemalloc.net/jemalloc.3.html
[jemalloc_wiki]: https://github.com/jemalloc/jemalloc/wiki
**Current jemalloc version**: 5.2.1.
## Platform support
See the platform support of the
[`jemallocator`](https://crates.io/crates/jemallocator) crate.
## Features
Most features correspond to `jemalloc` features - the reference is
[`jemalloc/INSTALL.md`][jemalloc_install].
### Cargo features
This crate provides following cargo feature flags:
* `profiling` (configure `jemalloc` with `--enable-prof`): Enable heap profiling
and leak detection functionality. See jemalloc's "opt.prof" option
documentation for usage details. When enabled, there are several approaches to
backtracing, and the configure script chooses the first one in the following
list that appears to function correctly:
* `libunwind` (requires --enable-prof-libunwind)
* `libgcc` (unless --disable-prof-libgcc)
* `gcc intrinsics` (unless --disable-prof-gcc)
* `stats` (configure `jemalloc` with `--enable-stats`): Enable statistics
gathering functionality. See the `jemalloc`'s "`opt.stats_print`" option
documentation for usage details.
* `debug` (configure `jemalloc` with `--enable-debug`): Enable assertions and
validation code. This incurs a substantial performance hit, but is very useful
during application development.
* `background_threads_runtime_support` (enabled by default): enables
background-threads run-time support when building `jemalloc-sys` on some POSIX
targets supported by `jemalloc`. Background threads are disabled at run-time
by default. This option allows dynamically enabling them at run-time.
* `background_threads` (disabled by default): enables background threads by
default at run-time. When set to true, background threads are created on
demand (the number of background threads will be no more than the number of
CPUs or active arenas). Threads run periodically, and handle purging
asynchronously. When switching off, background threads are terminated
synchronously. Note that after `fork(2)` function, the state in the child
process will be disabled regardless the state in parent process. See
`stats.background_thread` for related stats. `opt.background_thread` can be
used to set the default option. The background thread is only available on
selected pthread-based platforms.
* `unprefixed_malloc_on_supported_platforms`: when disabled, configure
`jemalloc` with `--with-jemalloc-prefix=_rjem_`. Enabling this causes symbols
like `malloc` to be emitted without a prefix, overriding the ones defined by
libc. This usually causes C and C++ code linked in the same program to use
`jemalloc` as well. On some platforms prefixes are always used because
unprefixing is known to cause segfaults due to allocator mismatches.
* `disable_initial_exec_tls` (disabled by default): when enabled, jemalloc is
built with the `--disable-initial-exec-tls` option. It disables the
initial-exec TLS model for jemalloc's internal thread-local storage (on those
platforms that support explicit settings). This can allow jemalloc to be
dynamically loaded after program startup (e.g. using dlopen). If you encounter
the error `yourlib.so: cannot allocate memory in static TLS block`, you'll
likely want to enable this.
* `disable_cache_oblivious` (disabled by default): when enabled, jemalloc is
built with the `--disable-cache-oblivious` option. In that case, all large
allocations are page-aligned as an implementation artifact. It may severely
harm CPU cache utilization. However, the cache-oblivious layout has a cost of
one extra page per large allocation which can be unfeasible for certain
applications.
### Environment variables
`jemalloc` options taking values are passed via environment variables using the
schema `JEMALLOC_SYS_{KEY}=VALUE` where the `KEY` names correspond to the
`./configure` options of `jemalloc` where the words are capitalized and the
hyphens `-` are replaced with underscores `_`(see
[`jemalloc/INSTALL.md`][jemalloc_install]):
* `JEMALLOC_SYS_WITH_MALLOC_CONF=<malloc_conf>`: Embed `<malloc_conf>` as a
run-time options string that is processed prior to the `malloc_conf` global
variable, the `/etc/malloc.conf` symlink, and the `MALLOC_CONF` environment
variable (note: this variable might be prefixed as `_RJEM_MALLOC_CONF`). For
example, to change the default decay time for dirty pages to 30 seconds:
```
JEMALLOC_SYS_WITH_MALLOC_CONF=dirty_decay_ms:30000
```
* `JEMALLOC_SYS_WITH_LG_PAGE=<lg-page>`: Specify the base 2 log of the allocator
page size, which must in turn be at least as large as the system page size. By
default the configure script determines the host's page size and sets the
allocator page size equal to the system page size, so this option need not be
specified unless the system page size may change between configuration and
execution, e.g. when cross compiling.
* `JEMALLOC_SYS_WITH_LG_HUGEPAGE=<lg-hugepage>`: Specify the base 2 log of the
system huge page size. This option is useful when cross compiling, or when
overriding the default for systems that do not explicitly support huge pages.
* `JEMALLOC_SYS_WITH_LG_QUANTUM=<lg-quantum>`: Specify the base 2 log of the
minimum allocation alignment. jemalloc needs to know the minimum alignment
that meets the following C standard requirement (quoted from the April 12,
2011 draft of the C11 standard):
> The pointer returned if the allocation succeeds is suitably aligned so that
> it may be assigned to a pointer to any type of object with a fundamental
> alignment requirement and then used to access such an object or an array of
> such objects in the space allocated [...]
This setting is architecture-specific, and although jemalloc includes known
safe values for the most commonly used modern architectures, there is a
wrinkle related to GNU libc (glibc) that may impact your choice of . On most
modern architectures, this mandates 16-byte alignment (=4), but the glibc
developers chose not to meet this requirement for performance reasons. An old
discussion can be found at https://sourceware.org/bugzilla/show_bug.cgi?id=206
. Unlike glibc, jemalloc does follow the C standard by default (caveat:
jemalloc technically cheats for size classes smaller than the quantum), but
the fact that Linux systems already work around this allocator noncompliance
means that it is generally safe in practice to let jemalloc's minimum
alignment follow glibc's lead. If you specify `JEMALLOC_SYS_WITH_LG_QUANTUM=3`
during configuration, jemalloc will provide additional size classes that are
not 16-byte-aligned (24, 40, and 56).
* `JEMALLOC_SYS_WITH_LG_VADDR=<lg-vaddr>`: Specify the number of significant
virtual address bits. By default, the configure script attempts to detect
virtual address size on those platforms where it knows how, and picks a
default otherwise. This option may be useful when cross-compiling.
[jemalloc_install]: https://github.com/jemalloc/jemalloc/blob/dev/INSTALL.md#advanced-configuration
## License
This project is licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or
http://opensource.org/licenses/MIT)
at your option.
## Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in `jemalloc-sys` by you, as defined in the Apache-2.0 license,
shall be dual licensed as above, without any additional terms or conditions.
[travis]: https://travis-ci.com/tikv/jemallocator
[Travis-CI Status]: https://travis-ci.com/tikv/jemallocator.svg?branch=master
[Latest Version]: https://img.shields.io/crates/v/jemallocator.svg
[crates.io]: https://crates.io/crates/jemallocator
[docs]: https://docs.rs/jemallocator/badge.svg
[docs.rs]: https://docs.rs/jemallocator/