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sync: document mpsc channel allocation behavior (#6773)

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Rafael Bachmann
2024-08-16 12:31:03 +02:00
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commit 5ea3c63d7e
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tokio/src/sync/mpsc/mod.rs
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@@ -78,6 +78,22 @@
//! within a Tokio runtime, however it is still not tied to one specific Tokio
//! runtime, and the sender may be moved from one Tokio runtime to another.
//!
//! # Allocation behavior
//!
//! <div class="warning">The implementation details described in this section may change in future
//! Tokio releases.</div>
//!
//! The mpsc channel stores elements in blocks. Blocks are organized in a linked list. Sending
//! pushes new elements onto the block at the front of the list, and receiving pops them off the
//! one at the back. A block can hold 32 messages on a 64-bit target and 16 messages on a 32-bit
//! target. This number is independent of channel and message size. Each block also stores 4
//! pointer-sized values for bookkeeping (so on a 64-bit machine, each message has 1 byte of
//! overhead).
//!
//! When all values in a block have been received, it becomes empty. It will then be freed, unless
//! the channel's first block (where newly-sent elements are being stored) has no next block. In
//! that case, the empty block is reused as the next block.
//!
//! [`Sender`]: crate::sync::mpsc::Sender
//! [`Receiver`]: crate::sync::mpsc::Receiver
//! [bounded-send]: crate::sync::mpsc::Sender::send()