modem: run the two OFDM decoders in parallel, one thread each

audioio/audioio.c

@@ -10,6 +10,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include <stdatomic.h>
 #include <limits.h>
 #include <errno.h>
 #include <signal.h>
@@ -32,7 +33,12 @@
 #include "resampler.h"
 #include "pcm24.h"
 
-extern volatile bool shutdown_;
+/* Must match the definition in common/mercury_engine.c: _Atomic, not
+ * volatile.  This global is written from the termination signal handler and
+ * polled by every worker loop; volatile orders nothing between threads, and
+ * declaring the same object differently in different translation units is
+ * undefined behaviour on top of that.  Plain assignment and test still work. */
+extern _Atomic bool shutdown_;
 
 /* ------------------------------------------------------------------ */
 /*  DirectSound GUID ↔ string helpers (Windows only)                  */

common/mercury_engine.c

@@ -33,7 +33,7 @@
 #include "virtual_clock.h"
 
 /* ---- shared globals ---- */
-volatile bool shutdown_ = false;
+_Atomic bool shutdown_ = false;
 static generic_modem_t g_modem;
 static pthread_t g_radio_capture, g_radio_playback;
 static int g_audio_system = -1;

common/mercury_engine.h

@@ -11,14 +11,20 @@
 #define MERCURY_ENGINE_H
 
 #include <stdbool.h>
+#include <stdatomic.h>
 #include <stdint.h>
 #include <pthread.h>
 
 #include "cfg_utils.h"
 #include "ui_communication.h"
 #include "modem.h"
 
-extern volatile bool shutdown_;
+/* Set by the termination signal handler, polled by main and by every worker
+ * loop.  _Atomic rather than volatile: volatile provides no inter-thread
+ * ordering, and the handler-write/thread-read pair is a data race in the
+ * formal sense (ThreadSanitizer reports it at main.c's handler).  Plain
+ * assignment and test still work -- C11 atomics overload them. */
+extern _Atomic bool shutdown_;
 
 /* ------------------------------------------------------------------ */
 /*  mercury_engine_init()                                              */

data_interfaces/tcp_interfaces.c

@@ -82,7 +82,12 @@ extern cbuf_handle_t data_rx_buffer_arq;
 extern cbuf_handle_t data_tx_buffer_broadcast;
 extern cbuf_handle_t data_rx_buffer_broadcast;
 
-extern volatile bool shutdown_;
+/* Must match the definition in common/mercury_engine.c: _Atomic, not
+ * volatile.  This global is written from the termination signal handler and
+ * polled by every worker loop; volatile orders nothing between threads, and
+ * declaring the same object differently in different translation units is
+ * undefined behaviour on top of that.  Plain assignment and test still work. */
+extern _Atomic bool shutdown_;
 
 extern arq_info arq_conn;
 

datalink_arq/arq.c

@@ -108,8 +108,14 @@ static pthread_t g_loop_tid;
 static pthread_t g_cmd_tid;
 static pthread_t g_payload_tid;
 
-static volatile bool g_running;
-static volatile bool g_initialized;
+/* Read by the modem RX/TX and TCP threads while the main thread writes them
+ * at init/teardown.  `volatile` orders nothing between threads and is not
+ * atomic in C -- formally a data race, and ThreadSanitizer flags exactly that
+ * (arq_init writing g_initialized against arq_get_runtime_snapshot reading it
+ * from the RX thread).  C11 atomics keep the plain read/write syntax, so only
+ * the declaration changes. */
+static _Atomic bool g_running;
+static _Atomic bool g_initialized;
 
 /* ======================================================================
  * Event queue helpers

datalink_broadcast/broadcast.c

@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdbool.h>
+#include <stdatomic.h>
 #include <unistd.h>
 #include <string.h>
 #include <pthread.h>
@@ -36,7 +37,12 @@
 #include "tcp_interfaces.h"
 #include "hermes_log.h"
 
-extern volatile bool shutdown_; // global shutdown flag
+/* Must match the definition in common/mercury_engine.c: _Atomic, not
+ * volatile.  This global is written from the termination signal handler and
+ * polled by every worker loop; volatile orders nothing between threads, and
+ * declaring the same object differently in different translation units is
+ * undefined behaviour on top of that.  Plain assignment and test still work. */
+extern _Atomic bool shutdown_;
 extern arq_info arq_conn; // ARQ connection info
 
 static const uint32_t hermes_broadcast_frame_size[] = { 510, 126, 14, 54, 14, 3, 30, 30, 14, 1180, 1213 };

gui_interface/ui_communication.c

@@ -29,6 +29,7 @@
 #include <time.h>
 #include <errno.h>
 #include <stdbool.h>
+#include <stdatomic.h>
 #include <math.h>
 
 #include "../common/os_interop.h"
@@ -53,7 +54,12 @@ extern int audioio_restart(const char *capture_dev, const char *playback_dev,
                            int audio_subsys, int capture_channel_layout);
 
 // global shutdown flag from main.c
-extern volatile bool shutdown_;
+/* Must match the definition in common/mercury_engine.c: _Atomic, not
+ * volatile.  This global is written from the termination signal handler and
+ * polled by every worker loop; volatile orders nothing between threads, and
+ * declaring the same object differently in different translation units is
+ * undefined behaviour on top of that.  Plain assignment and test still work. */
+extern _Atomic bool shutdown_;
 
 #define UI_LOG_TAG "ui-comm"