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If there is exactly one producer, then it can assume that the remaining space in the buffer will only increase until it write something. This assumption may allow the producer to write to the buffer (up to a known safe size) without any synchronization mechanism, thus allowing to read and write different parts of the buffer in parallel. The producer can then commit the write with lock held, and update its knowledge of the safe empty remaining space.
105 lines
2.7 KiB
C
105 lines
2.7 KiB
C
#ifndef SC_BYTEBUF_H
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#define SC_BYTEBUF_H
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#include "common.h"
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#include <stdbool.h>
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#include <stdint.h>
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struct sc_bytebuf {
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uint8_t *data;
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// The actual capacity is (allocated - 1) so that head == tail is
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// non-ambiguous
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size_t alloc_size;
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size_t head;
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size_t tail;
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// empty: tail == head
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// full: (tail + 1) % allocated == head
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};
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bool
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sc_bytebuf_init(struct sc_bytebuf *buf, size_t alloc_size);
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/**
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* Copy from the bytebuf to a user-provided array
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*
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* The caller must check that len <= buf->len (it is an error to attempt to read
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* more bytes than available).
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*
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* This function is guaranteed to not change the head.
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*/
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void
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sc_bytebuf_read(struct sc_bytebuf *buf, uint8_t *to, size_t len);
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/**
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* Drop len bytes from the buffer
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*
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* The caller must check that len <= buf->len (it is an error to attempt to skip
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* more bytes than available).
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*
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* This function is guaranteed to not change the head.
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*
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* It is equivalent to call sc_bytebuf_read() to some array and discard the
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* array (but more efficient since there is no copy).
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*/
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void
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sc_bytebuf_skip(struct sc_bytebuf *buf, size_t len);
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/**
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* Copy the user-provided array to the bytebuf
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*
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* The length of the input array is not restricted:
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* if len >= sc_bytebuf_write_remaining(buf), then the excessive input bytes
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* will overwrite the oldest bytes in the buffer.
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*/
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void
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sc_bytebuf_write(struct sc_bytebuf *buf, const uint8_t *from, size_t len);
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/**
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* Copy the user-provided array to the bytebuf, but do not advance the cursor
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*
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* The caller must check that len <= buf->len (it is an error to attempt to
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* write more bytes than available).
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*
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* After this function is called, the write must be committed with
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* sc_bytebuf_commit_write().
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*
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* The purpose of this mechanism is to acquire a lock only to commit the write,
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* but not to perform the actual copy.
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*/
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void
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sc_bytebuf_prepare_write(struct sc_bytebuf *buf, const uint8_t *from,
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size_t len);
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/**
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* Commit a prepared write
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*/
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void
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sc_bytebuf_commit_write(struct sc_bytebuf *buf, size_t len);
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/**
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* Return the number of bytes which can be read
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*
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* It is an error to read more bytes than available.
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*/
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static inline size_t
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sc_bytebuf_read_remaining(struct sc_bytebuf *buf) {
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return (buf->alloc_size + buf->head - buf->tail) % buf->alloc_size;
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}
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/**
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* Return the number of bytes which can be written without overwriting
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*
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* It is not an error to write more bytes than the available space, but this
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* would overwrite the oldest bytes in the buffer.
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*/
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static inline size_t
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sc_bytebuf_write_remaining(struct sc_bytebuf *buf) {
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return (buf->alloc_size + buf->tail - buf->head - 1) % buf->alloc_size;
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}
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void
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sc_bytebuf_destroy(struct sc_bytebuf *buf);
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#endif
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