4e6941e632
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. PR #3757 <https://github.com/Genymobile/scrcpy/pull/3757>
106 lines
2.8 KiB
C
106 lines
2.8 KiB
C
#include "bytebuf.h"
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#include <assert.h>
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#include <stdlib.h>
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#include <string.h>
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#include "util/log.h"
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bool
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sc_bytebuf_init(struct sc_bytebuf *buf, size_t alloc_size) {
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assert(alloc_size);
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// sufficient, but use more for alignment.
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buf->data = malloc(alloc_size);
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if (!buf->data) {
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LOG_OOM();
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return false;
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}
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buf->alloc_size = alloc_size;
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buf->head = 0;
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buf->tail = 0;
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return true;
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}
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void
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sc_bytebuf_destroy(struct sc_bytebuf *buf) {
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free(buf->data);
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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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assert(len);
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assert(len <= sc_bytebuf_read_available(buf));
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assert(buf->tail != buf->head); // the buffer could not be empty
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size_t right_limit = buf->tail < buf->head ? buf->head : buf->alloc_size;
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size_t right_len = right_limit - buf->tail;
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if (len < right_len) {
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right_len = len;
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}
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memcpy(to, buf->data + buf->tail, right_len);
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if (len > right_len) {
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memcpy(to + right_len, buf->data, len - right_len);
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}
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buf->tail = (buf->tail + len) % buf->alloc_size;
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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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assert(len);
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assert(len <= sc_bytebuf_read_available(buf));
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assert(buf->tail != buf->head); // the buffer could not be empty
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buf->tail = (buf->tail + len) % buf->alloc_size;
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}
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static inline void
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sc_bytebuf_write_step0(struct sc_bytebuf *buf, const uint8_t *from,
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size_t len) {
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size_t right_len = buf->alloc_size - buf->head;
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if (len < right_len) {
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right_len = len;
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}
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memcpy(buf->data + buf->head, from, right_len);
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if (len > right_len) {
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memcpy(buf->data, from + right_len, len - right_len);
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}
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}
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static inline void
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sc_bytebuf_write_step1(struct sc_bytebuf *buf, size_t len) {
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buf->head = (buf->head + len) % buf->alloc_size;
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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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assert(len);
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assert(len <= sc_bytebuf_write_available(buf));
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sc_bytebuf_write_step0(buf, from, len);
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sc_bytebuf_write_step1(buf, len);
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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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// *This function MUST NOT access buf->tail (even in assert()).*
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// The purpose of this function is to allow a reader and a writer to access
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// different parts of the buffer in parallel simultaneously. It is intended
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// to be called without lock (only sc_bytebuf_commit_write() is intended to
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// be called with lock held).
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assert(len < buf->alloc_size - 1);
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sc_bytebuf_write_step0(buf, from, len);
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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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assert(len <= sc_bytebuf_write_available(buf));
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sc_bytebuf_write_step1(buf, len);
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}
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