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forgectrl: streams preempt - the newest camera request wins the mux

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A stream request for the other camera kicks current stream clients via a generation counter (their streams end cleanly; viewers freeze on the last frame) and switches. The index page retry consults /cam/status first so a preempted view does not steal the camera back.
This commit is contained in:
ScottW514
2026-08-03 12:47:16 -04:00
parent 247cfacb40
commit dc34fc6602
4 changed files with 55 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files
meta-forgefirm/recipes-forgefirm/forgectrl/forgectrl/cam.c
+17 -7
View File
@@ -91,6 +91,8 @@ static struct {
cam_id_t home_cam; /* camera the engine serves for streaming -
* what arbitration must compare against */
int clients;
uint64_t kick_gen; /* bumped to preempt all current stream
* clients (their streams end cleanly) */
struct timespec last_activity;
/* published stream frame (half-res JPEG) */
@@ -727,9 +729,15 @@ static int ensure_engine(cam_id_t cam, char *err, size_t errlen)
if (running && cur != cam) {
if (clients > 0) {
/* Grace: a client that just disconnected releases its pin
* only when the MHD send fails on the next frame - absorb
* that (page navigations) instead of failing instantly. */
/* Last request wins: preempt the current stream clients
* (single-operator machine - the newest ask is the
* operator). Kicked clients wake, end their streams
* cleanly (viewers freeze on their last frame), and
* release their pins; wait for that to drain. */
pthread_mutex_lock(&eng.lock);
eng.kick_gen++;
pthread_cond_broadcast(&eng.frame_cv);
pthread_mutex_unlock(&eng.lock);
struct timespec t0, t;
now_ts(&t0);
do {
@@ -741,8 +749,8 @@ static int ensure_engine(cam_id_t cam, char *err, size_t errlen)
} while (clients > 0 && ts_diff(&t, &t0) < SWITCH_GRACE_S);
if (clients > 0) {
snprintf(err, errlen,
"camera busy: %d client(s) streaming %s",
clients, camdefs[cur].name);
"camera switch timed out: %d client(s) still "
"attached to %s", clients, camdefs[cur].name);
return -1;
}
}
@@ -878,6 +886,7 @@ int cam_snapshot(cam_id_t cam, int full, int quality,
struct cam_client {
uint64_t last_seq;
uint64_t gen; /* kick generation at open; a bump ends the stream */
uint8_t *buf;
size_t cap;
};
@@ -897,6 +906,7 @@ cam_client_t *cam_client_open(cam_id_t cam, char *err, size_t errlen)
}
pthread_mutex_lock(&eng.lock);
eng.clients++;
c->gen = eng.kick_gen;
now_ts(&eng.last_activity);
pthread_mutex_unlock(&eng.lock);
pthread_mutex_unlock(&eng.ctl);
@@ -907,7 +917,7 @@ long cam_client_next(cam_client_t *c, const uint8_t **jpeg)
{
pthread_mutex_lock(&eng.lock);
int timeouts = 0;
while (eng.running && eng.seq <= c->last_seq) {
while (eng.running && c->gen == eng.kick_gen && eng.seq <= c->last_seq) {
struct timespec deadline;
clock_gettime(CLOCK_REALTIME, &deadline);
deadline.tv_sec += CLIENT_WAIT_S;
@@ -915,7 +925,7 @@ long cam_client_next(cam_client_t *c, const uint8_t **jpeg)
== ETIMEDOUT && ++timeouts >= 2)
break;
}
if (!eng.running || eng.seq <= c->last_seq) {
if (!eng.running || c->gen != eng.kick_gen || eng.seq <= c->last_seq) {
pthread_mutex_unlock(&eng.lock);
return -1;
}
meta-forgefirm/recipes-forgefirm/forgectrl/forgectrl/cam.h
+5 -3
View File
@@ -36,9 +36,11 @@ void cam_engine_shutdown(void);
int cam_snapshot(cam_id_t cam, int full, int quality,
uint8_t **jpeg, size_t *len, char *err, size_t errlen);
/* Stream client: open pins the engine to a camera (starting or switching it
* if needed), next blocks for a frame newer than the last one returned and
* copies it into a client-owned buffer, close releases the pin. */
/* Stream client: open makes the engine serve `cam` (starting it, or
* preempting the current clients and switching - last request wins; the
* preempted clients' next() returns -1 so their streams end cleanly).
* next blocks for a frame newer than the last one returned and copies it
* into a client-owned buffer, close releases the pin. */
typedef struct cam_client cam_client_t;
cam_client_t *cam_client_open(cam_id_t cam, char *err, size_t errlen);
meta-forgefirm/recipes-forgefirm/forgectrl/forgectrl/main.c
+16 -10
View File
@@ -12,11 +12,11 @@
* GET /cam/snapshot?cam=&res=full|half&q= single JPEG (default full res)
* GET /cam/status JSON engine status
*
* The two cameras share the hardware mux, so streaming clients pin the
* selection: a STREAM request for the other camera waits a short grace
* for the pin to drain, then returns 409. A SNAPSHOT of the other camera
* never fails busy - the engine borrows the mux for one frame and the
* stream freezes for a few seconds instead.
* The two cameras share the hardware mux; the newest request wins it. A
* STREAM request for the other camera preempts the current stream
* clients (their streams end cleanly - viewers freeze on the last frame)
* and switches. A SNAPSHOT of the other camera does not switch: the
* engine borrows the mux for one frame and the stream freezes briefly.
* Environment: FORGECTRL_PORT (8080), FORGECTRL_STREAM_Q (75),
* FORGECTRL_LAMP (132).
*
@@ -246,11 +246,17 @@ static const char index_html[] =
"msg=document.getElementById('msg');"
"function setCam(c){cam=c;retries=0;msg.textContent='';"
"v.src='/cam/stream?cam='+c+'&t='+Date.now();}"
"v.onerror=function(){if(retries++<5){"
"msg.textContent='stream retrying...';"
"setTimeout(function(){v.src='/cam/stream?cam='+cam+'&t='+Date.now();},"
"700);}else{msg.textContent="
"'stream unavailable (camera busy from another viewer?)';}};"
"function reload(){v.src='/cam/stream?cam='+cam+'&t='+Date.now();}"
/* Retry only when the engine still serves our camera - if another
* viewer preempted it, retrying would steal it right back. */
"v.onerror=function(){fetch('/cam/status').then(function(r){"
"return r.json();}).then(function(s){"
"if(s.cam===cam&&retries++<5){msg.textContent='stream retrying...';"
"setTimeout(reload,700);}else if(s.cam!==cam){msg.textContent="
"'stream taken by another viewer ('+s.cam+') - press a button to resume';}"
"else{msg.textContent='stream error - press a stream button to retry';}"
"}).catch(function(){msg.textContent="
"'service unreachable';});};"
"function peek(){"
"msg.textContent='head peek (stream pauses a few seconds)...';"
"p.style.display='inline';p.onload=function(){msg.textContent='';};"