Remove callback from cosmoaudio API

Using callbacks is still problematic with cosmo_dlopen() due to the need
to restore the TLS register. So using callbacks is even more strict than
using signal handlers. We are better off introducing a cosmoaudio_poll()
function. It makes the API more UNIX-like. How bad could the latency be?

Makefile

@@ -493,6 +493,7 @@ COSMOPOLITAN_OBJECTS =			\
 
 COSMOPOLITAN_H_PKGS =			\
 	APE				\
+	DSP_AUDIO			\
 	LIBC				\
 	LIBC_CALLS			\
 	LIBC_ELF			\

dsp/audio/audio.c

@@ -58,7 +58,9 @@ static struct {
   typeof(cosmoaudio_open) *open;
   typeof(cosmoaudio_close) *close;
   typeof(cosmoaudio_write) *write;
+  typeof(cosmoaudio_flush) *flush;
   typeof(cosmoaudio_read) *read;
+  typeof(cosmoaudio_poll) *poll;
 } g_audio;
 
 static const char *cosmoaudio_tmp_dir(void) {
@@ -232,7 +234,9 @@ static void cosmoaudio_setup(void) {
   g_audio.open = cosmo_dlsym(handle, "cosmoaudio_open");
   g_audio.close = cosmo_dlsym(handle, "cosmoaudio_close");
   g_audio.write = cosmo_dlsym(handle, "cosmoaudio_write");
+  g_audio.flush = cosmo_dlsym(handle, "cosmoaudio_flush");
   g_audio.read = cosmo_dlsym(handle, "cosmoaudio_read");
+  g_audio.poll = cosmo_dlsym(handle, "cosmoaudio_poll");
 }
 
 static void cosmoaudio_init(void) {
@@ -295,3 +299,34 @@ COSMOAUDIO_ABI int cosmoaudio_read(struct CosmoAudio *ca, float *data,
               cosmoaudio_describe_status(sbuf, sizeof(sbuf), status));
   return status;
 }
+
+COSMOAUDIO_ABI int cosmoaudio_flush(struct CosmoAudio *ca) {
+  int status;
+  char sbuf[32];
+  if (g_audio.flush)
+    status = g_audio.flush(ca);
+  else
+    status = COSMOAUDIO_ELINK;
+  DATATRACE("cosmoaudio_flush(%p) → %s", ca,
+            cosmoaudio_describe_status(sbuf, sizeof(sbuf), status));
+  return status;
+}
+
+COSMOAUDIO_ABI int cosmoaudio_poll(struct CosmoAudio *ca,
+                                   int *in_out_readFrames,
+                                   int *in_out_writeFrames) {
+  int status;
+  char sbuf[32];
+  char fbuf[2][20];
+  if (g_audio.poll)
+    status = g_audio.poll(ca, in_out_readFrames, in_out_writeFrames);
+  else
+    status = COSMOAUDIO_ELINK;
+  DATATRACE("cosmoaudio_poll(%p, %s, %s) → %s", ca,
+            cosmoaudio_describe_poll_frames(fbuf[0], sizeof(fbuf[0]),
+                                            in_out_readFrames),
+            cosmoaudio_describe_poll_frames(fbuf[1], sizeof(fbuf[1]),
+                                            in_out_writeFrames),
+            cosmoaudio_describe_status(sbuf, sizeof(sbuf), status));
+  return status;
+}

dsp/audio/cosmoaudio/Makefile.msvc

@@ -3,6 +3,7 @@
 #     nmake /f Makefile.msvc check
 #     nmake /f Makefile.msvc MODE=debug check
 #
+# Note: MSVC 2019 makes the DLL 64kb smaller than MSVC 2022.
 
 # Compiler and linker
 CC=cl