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ring_buffer: simplify write overflow detection

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This commit is contained in:
Martin Piatka
2021-08-26 15:30:12 +02:00
parent f796e62e16
commit 6bf2b60839
1 changed files with 34 additions and 34 deletions
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68
src/utils/ring_buffer.cpp
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@@ -105,29 +105,29 @@ void ring_buffer_flush(struct ring_buffer * buf) {
buf->end = 0;
}
static int calculate_avail_read(int start, int end, int buf_len){
return (end - start + buf_len) % buf_len;
}
static int calculate_avail_write(int start, int end, int buf_len){
/* Ring buffer needs at least one free byte, otherwise start == end
* and the ring would appear empty */
return buf_len - calculate_avail_read(start, end, buf_len) - 1;
}
void ring_buffer_write(struct ring_buffer * ring, const char *in, int len) {
int start = std::atomic_load_explicit(&ring->start, std::memory_order_acquire);
// end index is modified only by this (writer) thread, so relaxed is enough
int end = std::atomic_load_explicit(&ring->start, std::memory_order_relaxed);
if(len > ring->len) {
fprintf(stderr, "Warning: too long write request for ring buffer (%d B)!!!\n", len);
return;
}
/* detect overrun */
{
int read_len_old = end - start;
int read_len_new = ((end + len) % ring->len) - start;
if(read_len_old < 0)
read_len_old += ring->len;
if(read_len_new < 0)
read_len_new += ring->len;
if(read_len_new < read_len_old) {
fprintf(stderr, "Warning: ring buffer overflow!!!\n");
}
if(len > calculate_avail_write(start, end, ring->len)) {
fprintf(stderr, "Warning: ring buffer overflow!!!\n");
}
int to_end = ring->len - end;
@@ -149,31 +149,31 @@ int ring_get_size(struct ring_buffer * ring) {
return ring->len;
}
int ring_get_current_size(struct ring_buffer * ring)
{
/* This is called from both reader and writer thread.
*
* Writer case:
* If the reader modifies start index under our feet, it doesn't
* matter, because reader can only make the current size smaller. That
* means the writer may calculate less free space, but never more than
* really available.
*
* Reader case:
* If the writer modifies end index under our feet, it doesn't matter,
* because the writer can only make current size bigger. That means the
* reader may calculate less size for reading, but the read data is
* always valid.
*/
/* ring_get_current_size and ring_get_available_write_size can be called from
* both reader and writer threads.
*
* Writer case:
* If the reader modifies start index under our feet, it doesn't
* matter, because reader can only make the current size smaller. That
* means the writer may calculate less free space, but never more than
* really available.
*
* Reader case:
* If the writer modifies end index under our feet, it doesn't matter,
* because the writer can only make current size bigger. That means the
* reader may calculate less size for reading, but the read data is
* always valid.
*/
int ring_get_current_size(struct ring_buffer * ring) {
int start = std::atomic_load_explicit(&ring->start, std::memory_order_acquire);
int end = std::atomic_load_explicit(&ring->end, std::memory_order_acquire);
return (end - start + ring->len) % ring->len;
return calculate_avail_read(start, end, ring->len);
}
int ring_get_available_write_size(struct ring_buffer * ring){
/* Ring buffer needs at least one free byte, otherwise start == end
* and the ring would appear empty */
return ring_get_size(ring) - ring_get_current_size(ring) - 1;
int ring_get_available_write_size(struct ring_buffer * ring) {
int start = std::atomic_load_explicit(&ring->start, std::memory_order_acquire);
int end = std::atomic_load_explicit(&ring->end, std::memory_order_acquire);
return calculate_avail_write(start, end, ring->len);
}
struct audio_buffer_api ring_buffer_fns = {