Struct chronicle::queue::BytesWriter

#[repr(C)]
pub struct BytesWriter { /* private fields */ }

Expand description

A BytesWriter enables a writer to directly access mutable bytes within a reserved section with explicit size at the current end of a Queue. In some cases this can result in reduced write latency by eliminating a copy. It also enables Queue to be directly integrated with components which write directly to memory.

A BytesWriter internally wraps a write DocumentContext, and so holds the Queue write lock for the duration of its scope. As with DocumentContext it is recommended to use the scoped form of BytesWriter which automatically handles closure when dropped.

The size of the section of queue reserved by a BytesWriter can be adjusted using resize, and similarly to DocumentContext write attempts can be abandoned using rollback_on_close without changing the state of the Queue.

Data written using a BytesWriter is normally read using a complementary BytesReader.

Example

let mut appender = queue.acquire_appender().unwrap();
{
    let mut writer = appender.scoped_bytes_writer(MSGSIZE);
    let slice = writer.as_mut().as_slice();
    ...
    // directly write to the slice (which writes directly to the Queue)
    ...
    // write lock released and write atomically committed as the writer goes out of scope
}

Implementations§

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impl BytesWriter

pub fn as_slice(self: Pin<&mut Self>) -> &mut [u8] ⓘ

Get a mutable slice to the reserved section of the Queue as a &mut [u8]

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impl BytesWriter

pub fn resize(self: Pin<&mut Self>, size: u64)

Resize the reserved section of the Queue wrapped by this BytesWriter

The reserved size can be extended as well as shrunk. The actual size of data written to the Queue will be the original size requested when creating the BytesWriter, or whichever size was passed to the most recent resize call.

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impl BytesWriter

pub fn rollback_on_close(self: Pin<&mut Self>)

Abandon a write. Any changes will be discarded when this BytesWriter goes out of scope, and the state of the Queue will be as it was before the BytesWriter was created.