* systems. There is no support for Microsoft Windows yet, and that will in
* fact probably an entirely separate program.
*
- * The program runs (at least) two threads. listen_thread() is responsible for
- * reading RTP packets off the wire and adding them to the binary heap @ref
- * packets, assuming they are basically sound.
+ * The program runs (at least) three threads. listen_thread() is responsible
+ * for reading RTP packets off the wire and adding them to the linked list @ref
+ * received_packets, assuming they are basically sound. queue_thread() takes
+ * packets off this linked list and adds them to @ref packets (an operation
+ * which might be much slower due to contention for @ref lock).
*
* The main thread is responsible for actually playing audio. In ALSA this
* means it waits until ALSA says it's ready for more audio which it then
* Sometimes it happens that there is no audio available to play. This may
* because the server went away, or a packet was dropped, or the server
* deliberately did not send any sound because it encountered a silence.
+ *
+ * Assumptions:
+ * - it is safe to read uint32_t values without a lock protecting them
*/
#include <config.h>
#include "defs.h"
#include "vector.h"
#include "heap.h"
+#include "timeval.h"
#if HAVE_COREAUDIO_AUDIOHARDWARE_H
# include <CoreAudio/AudioHardware.h>
* timestamp.
*/
struct packet {
+ /** @brief Next packet in @ref next_free_packet or @ref received_packets */
+ struct packet *next;
+
/** @brief Number of samples in this packet */
uint32_t nsamples;
return lt(a->timestamp, b->timestamp);
}
+/** @brief Received packets
+ * Protected by @ref receive_lock
+ *
+ * Received packets are added to this list, and queue_thread() picks them off
+ * it and adds them to @ref packets. Whenever a packet is added to it, @ref
+ * receive_cond is signalled.
+ */
+static struct packet *received_packets;
+
+/** @brief Tail of @ref received_packets
+ * Protected by @ref receive_lock
+ */
+static struct packet **received_tail = &received_packets;
+
+/** @brief Lock protecting @ref received_packets
+ *
+ * Only listen_thread() and queue_thread() ever hold this lock. It is vital
+ * that queue_thread() not hold it any longer than it strictly has to. */
+static pthread_mutex_t receive_lock = PTHREAD_MUTEX_INITIALIZER;
+
+/** @brief Condition variable signalled when @ref received_packets is updated
+ *
+ * Used by listen_thread() to notify queue_thread() that it has added another
+ * packet to @ref received_packets. */
+static pthread_cond_t receive_cond = PTHREAD_COND_INITIALIZER;
+
+/** @brief Length of @ref received_packets */
+static uint32_t nreceived;
+
/** @struct pheap
* @brief Binary heap of packets ordered by timestamp */
HEAP_TYPE(pheap, struct packet *, lt_packet);
/** @brief Binary heap of received packets */
static struct pheap packets;
-/** @brief Total number of samples available */
-static unsigned long nsamples;
+/** @brief Total number of samples available
+ *
+ * We make this volatile because we inspect it without a protecting lock,
+ * so the usual pthread_* guarantees aren't available.
+ */
+static volatile uint32_t nsamples;
/** @brief Timestamp of next packet to play.
*
* This is true when playing and false when just buffering. */
static int active;
+/** @brief Lock protecting @ref packets */
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+
+/** @brief Condition variable signalled whenever @ref packets is changed */
+static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+
/** @brief Structure of free packet list */
union free_packet {
struct packet p;
*/
static size_t count_free_packets;
-/** @brief Lock protecting @ref packets
- *
- * This also protects the packet memory allocation infrastructure, @ref
- * free_packets and @ref next_free_packet. */
-static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
-
-/** @brief Condition variable signalled whenever @ref packets is changed */
-static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+/** @brief Lock protecting packet allocator */
+static pthread_mutex_t mem_lock = PTHREAD_MUTEX_INITIALIZER;
static const struct option options[] = {
{ "help", no_argument, 0, 'h' },
{ 0, 0, 0, 0 }
};
-/** @brief Return a new packet
- *
- * Assumes that @ref lock is held. */
+/** @Brief Return a new packet */
static struct packet *new_packet(void) {
struct packet *p;
-
+
+ pthread_mutex_lock(&mem_lock);
if(free_packets) {
p = &free_packets->p;
free_packets = free_packets->next;
p = &(next_free_packet++)->p;
--count_free_packets;
}
+ pthread_mutex_unlock(&mem_lock);
return p;
}
-/** @brief Free a packet
- *
- * Assumes that @ref lock is held. */
+/** @brief Free a packet */
static void free_packet(struct packet *p) {
union free_packet *u = (union free_packet *)p;
+ pthread_mutex_lock(&mem_lock);
u->next = free_packets;
free_packets = u;
+ pthread_mutex_unlock(&mem_lock);
}
/** @brief Drop the first packet
}
}
+/** @brief Background thread adding packets to heap
+ *
+ * This just transfers packets from @ref received_packets to @ref packets. It
+ * is important that it holds @ref receive_lock for as little time as possible,
+ * in order to minimize the interval between calls to read() in
+ * listen_thread().
+ */
+static void *queue_thread(void attribute((unused)) *arg) {
+ struct packet *p;
+
+ for(;;) {
+ /* Get the next packet */
+ pthread_mutex_lock(&receive_lock);
+ while(!received_packets)
+ pthread_cond_wait(&receive_cond, &receive_lock);
+ p = received_packets;
+ received_packets = p->next;
+ if(!received_packets)
+ received_tail = &received_packets;
+ --nreceived;
+ pthread_mutex_unlock(&receive_lock);
+ /* Add it to the heap */
+ pthread_mutex_lock(&lock);
+ pheap_insert(&packets, p);
+ nsamples += p->nsamples;
+ pthread_cond_broadcast(&cond);
+ pthread_mutex_unlock(&lock);
+ }
+}
+
/** @brief Background thread collecting samples
*
* This function collects samples, perhaps converts them to the target format,
struct iovec iov[2];
for(;;) {
- if(!p) {
- pthread_mutex_lock(&lock);
+ if(!p)
p = new_packet();
- pthread_mutex_unlock(&lock);
- }
iov[0].iov_base = &header;
iov[0].iov_len = sizeof header;
iov[1].iov_base = p->samples_raw;
timestamp, next_timestamp);
continue;
}
- pthread_mutex_lock(&lock);
+ p->next = 0;
p->flags = 0;
p->timestamp = timestamp;
/* Convert to target format */
* This is rather unsatisfactory: it means that if packets get heavily
* out of order then we guarantee dropouts. But for now... */
if(nsamples >= maxbuffer) {
- //info("Buffer full");
- write(2, "B", 1);
+ pthread_mutex_lock(&lock);
while(nsamples >= maxbuffer)
pthread_cond_wait(&cond, &lock);
+ pthread_mutex_unlock(&lock);
}
- /* Add the packet to the heap */
- pheap_insert(&packets, p);
- nsamples += p->nsamples;
+ /* Add the packet to the receive queue */
+ pthread_mutex_lock(&receive_lock);
+ *received_tail = p;
+ received_tail = &p->next;
+ ++nreceived;
+ pthread_cond_signal(&receive_cond);
+ pthread_mutex_unlock(&receive_lock);
/* We'll need a new packet */
p = 0;
- pthread_cond_broadcast(&cond);
- pthread_mutex_unlock(&lock);
}
}
while(samplesOutLeft > 0) {
const struct packet *p = next_packet();
if(p && contains(p, next_timestamp)) {
- if(p->flags & IDLE)
- write(2, "I", 1);
/* This packet is ready to play */
const uint32_t packet_end = p->timestamp + p->nsamples;
const uint32_t offset = next_timestamp - p->timestamp;
*samplesOut++ = (int16_t)ntohs(*ptr++) * (0.5 / 32767);
/* We don't bother junking the packet - that'll be dealt with next time
* round */
- write(2, ".", 1);
} else {
/* No packet is ready to play (and there might be no packet at all) */
samples_available = p ? p->timestamp - next_timestamp
next_timestamp += samples_available;
samplesOut += samples_available;
samplesOutLeft -= samples_available;
- write(2, "?", 1);
}
}
++ab;
/* Something went wrong */
switch(frames_written) {
case -EAGAIN:
- write(2, "#", 1);
return 0;
case -EPIPE:
error(0, "error calling snd_pcm_writei: %ld",
* @return 0 on success, -1 on non-fatal error
*/
static int alsa_play(const struct packet *p) {
- if(p->flags & IDLE)
- write(2, "I", 1);
- write(2, ".", 1);
return alsa_writei(p->samples_raw + next_timestamp - p->timestamp,
(p->timestamp + p->nsamples) - next_timestamp);
}
if(p && samples_available > p->timestamp - next_timestamp)
samples_available = p->timestamp - next_timestamp;
- write(2, "?", 1);
return alsa_writei(zeros, samples_available);
}
/* We receive and convert audio data in a background thread */
pthread_create(<id, 0, listen_thread, 0);
+ /* We have a second thread to add received packets to the queue */
+ pthread_create(<id, 0, queue_thread, 0);
#if API_ALSA
{
struct packet *p;
~mdw / disorder / commitdiff