Compromise on the blocking open() call with certain OSS drivers. The

workaround is now turned off by default.  If the --enable-broken-oss
option is passed to configure or if ALSA is detected, the workaround is
turned on during compilation.  This will resolve bug 48.


git-svn-id: http://svn.xiph.org/trunk/ao@2146 0101bb08-14d6-0310-b084-bc0e0c8e3800

README

@@ -51,3 +51,15 @@ could be provided.  The API was revised for version 0.8.0.
 This code is being maintained by Stan Seibert (indigo@aztec.asu.edu) 
 and various other individuals.  Please DO NOT annoy Aaron Holtzman about 
 bugs, features, comments, etc. regarding this code.
+
+WORKAROUNDS
+
+The OSS emulation in ALSA deviates from the OSS spec by not returning
+immediately from an open() call if the OSS device is already in use.
+Instead, it makes the application wait until the device is available.
+This is not desirable during the autodetection phase of libao, so a
+workaround has been included in the source.  Since the workaround
+itself violates the OSS spec and causes other problems on some
+platforms, it is only enabled when ALSA is detected.  The workaround
+can be turned on or off by passing the --enable-broken-oss or
+--disable-broken-oss flag to the configure script.

configure.in

@@ -196,7 +196,19 @@ else
 fi
 AC_SUBST(ALSA09_LIBS)
 
+dnl Decide whether we need to enable the workaround for broken OSS APIs
+dnl such as the OSS emulation in ALSA.
 
+AC_ARG_ENABLE(broken-oss, [  --enable-broken-oss           workaround for some OSS drivers (see README for details)],,
+if test "x$have_alsa" = "xyes" -o "x$have_alsa09" = "xyes"; then
+   enable_broken_oss="yes"
+fi)
+
+if test "x$enable_broken_oss" = "xyes"; then
+   AC_DEFINE(BROKEN_OSS)
+   AC_MSG_WARN(Broken OSS API workaround enabled.  See README for details.)
+fi
+   
 dnl Check for Sun audio
 
 AC_CHECK_HEADERS(sys/audioio.h)

src/plugins/oss/ao_oss.c

@@ -70,10 +70,11 @@ typedef struct ao_oss_internal {
  * *dev_path.  Assumes that *dev_path does not need to be free()'ed
  * initially.
  *
- * This opens the device in non-blocking mode at first in order to prevent
- * deadlock caused by ALSA's OSS emulation and some OSS drivers if the
- * device is already in use.  If blocking is non-zero, we remove the blocking
- * flag if possible so that the device can be used for actual output.
+ * If BROKEN_OSS is defined, this opens the device in non-blocking
+ * mode at first in order to prevent deadlock caused by ALSA's OSS
+ * emulation and some OSS drivers if the device is already in use.  If
+ * blocking is non-zero, we remove the blocking flag if possible so
+ * that the device can be used for actual output.
  */
 int _open_default_oss_device (char **dev_path, int blocking)
 {
@@ -83,7 +84,11 @@ int _open_default_oss_device (char **dev_path, int blocking)
 
 	/* default: first try the devfs path */
 	*dev_path = strdup("/dev/sound/dsp");
+#ifdef BROKEN_OSS
 	fd = open(*dev_path, O_WRONLY | O_NONBLOCK);
+#else
+	fd = open(*dev_path, O_WRONLY);
+#endif /* BROKEN_OSS */
 
 	/* then try the original dsp path */
 	if(fd < 0) 
@@ -93,9 +98,14 @@ int _open_default_oss_device (char **dev_path, int blocking)
 		dev = strdup(*dev_path);
 		free(*dev_path);
 		*dev_path = strdup("/dev/dsp");
+#ifdef BROKEN_OSS
 		fd = open(*dev_path, O_WRONLY | O_NONBLOCK);
+#else
+		fd = open(*dev_path, O_WRONLY);
+#endif /* BROKEN_OSS */
 	}
 
+#ifdef BROKEN_OSS
 	/* Now have to remove the O_NONBLOCK flag if so instructed. */
 	if (fd > 0 && blocking) {
 		if (fcntl(fd, F_SETFL, 0) < 0) { /* Remove O_NONBLOCK */
@@ -105,6 +115,7 @@ int _open_default_oss_device (char **dev_path, int blocking)
 			fd = -1;
 		}
 	}
+#endif /* BROKEN_OSS */
 
 	/* Deal with error cases */
 	if(fd < 0)