Struct memmap2::MmapRaw

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pub struct MmapRaw { /* private fields */ }

Expand description

A handle to a raw memory mapped buffer.

This struct never hands out references to its interior, only raw pointers. This can be helpful when creating shared memory maps between untrusted processes.

For the safety concerns that arise when converting these raw pointers to references, see the Mmap safety documentation.

Implementations§

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impl MmapRaw

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pub fn map_raw<T: MmapAsRawDesc>(file: T) -> Result<MmapRaw>

Creates a writeable memory map backed by a file.

This is equivalent to calling MmapOptions::new().map_raw(file).

§Errors

This method returns an error when the underlying system call fails, which can happen for a variety of reasons, such as when the file is not open with read and write permissions.

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pub fn as_ptr(&self) -> *const u8

Returns a raw pointer to the memory mapped file.

Before dereferencing this pointer, you have to make sure that the file has not been truncated since the memory map was created. Avoiding this will not introduce memory safety issues in Rust terms, but will cause SIGBUS (or equivalent) signal.

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pub fn as_mut_ptr(&self) -> *mut u8

Returns an unsafe mutable pointer to the memory mapped file.

Before dereferencing this pointer, you have to make sure that the file has not been truncated since the memory map was created. Avoiding this will not introduce memory safety issues in Rust terms, but will cause SIGBUS (or equivalent) signal.

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pub fn len(&self) -> usize

Returns the length in bytes of the memory map.

Note that truncating the file can cause the length to change (and render this value unusable).

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pub fn flush(&self) -> Result<()>

Flushes outstanding memory map modifications to disk.

When this method returns with a non-error result, all outstanding changes to a file-backed memory map are guaranteed to be durably stored. The file’s metadata (including last modification timestamp) may not be updated.

§Example

use std::fs::OpenOptions;
use std::io::Write;
use std::path::PathBuf;
use std::slice;

use memmap2::MmapRaw;

let tempdir = tempfile::tempdir()?;
let path: PathBuf = /* path to file */
let file = OpenOptions::new().read(true).write(true).create(true).open(&path)?;
file.set_len(128)?;

let mut mmap = unsafe { MmapRaw::map_raw(&file)? };

let mut memory = unsafe { slice::from_raw_parts_mut(mmap.as_mut_ptr(), 128) };
memory.write_all(b"Hello, world!")?;
mmap.flush()?;

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pub fn flush_async(&self) -> Result<()>

Asynchronously flushes outstanding memory map modifications to disk.

This method initiates flushing modified pages to durable storage, but it will not wait for the operation to complete before returning. The file’s metadata (including last modification timestamp) may not be updated.

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pub fn flush_range(&self, offset: usize, len: usize) -> Result<()>

Flushes outstanding memory map modifications in the range to disk.

The offset and length must be in the bounds of the memory map.

When this method returns with a non-error result, all outstanding changes to a file-backed memory in the range are guaranteed to be durable stored. The file’s metadata (including last modification timestamp) may not be updated. It is not guaranteed the only the changes in the specified range are flushed; other outstanding changes to the memory map may be flushed as well.

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pub fn flush_async_range(&self, offset: usize, len: usize) -> Result<()>

Asynchronously flushes outstanding memory map modifications in the range to disk.

The offset and length must be in the bounds of the memory map.

This method initiates flushing modified pages to durable storage, but it will not wait for the operation to complete before returning. The file’s metadata (including last modification timestamp) may not be updated. It is not guaranteed that the only changes flushed are those in the specified range; other outstanding changes to the memory map may be flushed as well.