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fifo.c
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fifo.c
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// Part of readsb, a Mode-S/ADSB/TIS message decoder.
//
// fifo.c: Cross-thread SDR to demodulator FIFO support
//
// This code is based on work as part of dump1090-fa.
//
// Copyright (c) 2020 FlightAware LLC
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
#include "fifo.h"
#include "util.h"
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <assert.h>
static pthread_mutex_t fifo_mutex = PTHREAD_MUTEX_INITIALIZER; // mutex protecting the queues
static pthread_cond_t fifo_notempty_cond = PTHREAD_COND_INITIALIZER; // condition used to signal FIFO-not-empty
static pthread_cond_t fifo_empty_cond = PTHREAD_COND_INITIALIZER; // condition used to signal FIFO-empty
static pthread_cond_t fifo_free_cond = PTHREAD_COND_INITIALIZER; // condition used to signal freelist-not-empty
static struct mag_buf *fifo_head; // head of queued buffers awaiting demodulation
static struct mag_buf *fifo_tail; // tail of queued buffers awaiting demodulation
static struct mag_buf *fifo_freelist; // freelist of preallocated buffers
static bool fifo_halted; // true if queue has been halted
static unsigned overlap_length; // desired overlap size in samples (size of overlap_buffer)
static uint16_t *overlap_buffer; // buffer used to save overlapping data
// Create the queue structures. Not threadsafe.
bool fifo_create(unsigned buffer_count, unsigned buffer_size, unsigned overlap) {
if (!(overlap_buffer = calloc(overlap, sizeof (overlap_buffer[0])))) {
goto nomem;
}
overlap_length = overlap;
for (unsigned i = 0; i < buffer_count; ++i) {
struct mag_buf *newbuf;
if (!(newbuf = calloc(1, sizeof (*newbuf)))) {
goto nomem;
}
if (!(newbuf->data = calloc(buffer_size, sizeof (newbuf->data[0])))) {
free(newbuf);
goto nomem;
}
newbuf->totalLength = buffer_size;
newbuf->next = fifo_freelist;
fifo_freelist = newbuf;
}
return true;
nomem:
fifo_destroy();
return false;
}
static void free_buffer_list(struct mag_buf *head) {
while (head) {
struct mag_buf *next = head->next;
free(head->data);
free(head);
head = next;
}
}
void fifo_destroy() {
free_buffer_list(fifo_head);
free_buffer_list(fifo_freelist);
fifo_freelist = NULL;
fifo_head = fifo_tail = NULL;
free(overlap_buffer);
overlap_buffer = NULL;
}
void fifo_drain() {
pthread_mutex_lock(&fifo_mutex);
while (fifo_head && !fifo_halted) {
pthread_cond_wait(&fifo_empty_cond, &fifo_mutex);
}
pthread_mutex_unlock(&fifo_mutex);
}
void fifo_halt() {
pthread_mutex_lock(&fifo_mutex);
// Drain all enqueued buffers to the freelist
while (fifo_head) {
struct mag_buf *freebuf = fifo_head;
fifo_head = freebuf->next;
freebuf->next = fifo_freelist;
fifo_freelist = freebuf;
}
fifo_tail = NULL;
fifo_halted = true;
// wake all waiters
pthread_cond_broadcast(&fifo_notempty_cond);
pthread_cond_broadcast(&fifo_empty_cond);
pthread_cond_broadcast(&fifo_free_cond);
pthread_mutex_unlock(&fifo_mutex);
}
struct mag_buf *fifo_acquire(uint32_t timeout_ms) {
struct timespec deadline;
if (timeout_ms) {
get_deadline(timeout_ms, &deadline);
}
pthread_mutex_lock(&fifo_mutex);
struct mag_buf *result = NULL;
while (!fifo_halted && !fifo_freelist) {
if (!timeout_ms) {
// Non-blocking
goto done;
}
// No free buffers, wait for one
if (pthread_cond_timedwait(&fifo_free_cond, &fifo_mutex, &deadline) < 0) {
if (errno != ETIMEDOUT)
return NULL; // unexpected error, mutex no longer held!
goto done; // timed out
}
}
if (!fifo_halted) {
result = fifo_freelist;
fifo_freelist = result->next;
result->overlap = overlap_length;
result->validLength = result->overlap;
result->sampleTimestamp = 0;
result->sysTimestamp = 0;
result->flags = 0;
result->next = NULL;
}
done:
pthread_mutex_unlock(&fifo_mutex);
return result;
}
void fifo_enqueue(struct mag_buf *buf) {
assert(buf->validLength <= buf->totalLength);
assert(buf->validLength >= overlap_length);
pthread_mutex_lock(&fifo_mutex);
if (fifo_halted) {
// Shutting down, just return the buffer to the freelist.
buf->next = fifo_freelist;
fifo_freelist = buf;
goto done;
}
// Populate the overlap region
if (buf->flags & MAGBUF_DISCONTINUOUS) {
// This buffer is discontinuous to the previous, so the overlap region is not valid; zero it out
memset(buf->data, 0, overlap_length * sizeof (buf->data[0]));
} else {
memcpy(buf->data, overlap_buffer, overlap_length * sizeof (buf->data[0]));
}
// Save the tail of the buffer for next time
memcpy(overlap_buffer, &buf->data[buf->validLength - overlap_length], overlap_length * sizeof (overlap_buffer[0]));
// enqueue and tell the main thread
buf->next = NULL;
if (!fifo_head) {
fifo_head = fifo_tail = buf;
pthread_cond_signal(&fifo_notempty_cond);
} else {
fifo_tail->next = buf;
}
done:
pthread_mutex_unlock(&fifo_mutex);
}
struct mag_buf *fifo_dequeue(uint32_t timeout_ms) {
struct timespec deadline;
if (timeout_ms) {
get_deadline(timeout_ms, &deadline);
}
pthread_mutex_lock(&fifo_mutex);
struct mag_buf *result = NULL;
while (!fifo_head && !fifo_halted) {
if (!timeout_ms) {
// Non-blocking
goto done;
}
// No data pending, wait for some
if (pthread_cond_timedwait(&fifo_notempty_cond, &fifo_mutex, &deadline) < 0) {
if (errno != ETIMEDOUT)
return NULL; // unexpected error, mutex no longer held!
goto done; // timed out
}
}
if (!fifo_halted) {
result = fifo_head;
fifo_head = result->next;
result->next = NULL;
if (!fifo_head) {
fifo_tail = NULL;
pthread_cond_broadcast(&fifo_empty_cond);
}
}
done:
pthread_mutex_unlock(&fifo_mutex);
return result;
}
void fifo_release(struct mag_buf *buf) {
pthread_mutex_lock(&fifo_mutex);
if (!fifo_freelist) {
pthread_cond_signal(&fifo_free_cond);
}
buf->next = fifo_freelist;
fifo_freelist = buf;
pthread_mutex_unlock(&fifo_mutex);
}