dshow: handle events in graph

Handling DirectShow events prevents infinite loops when there is an error in
the graph, such as a device being disconnected. This makes it possible for
dshow to return an error to the caller and run the cleanup code.

Based on patch by Don Moir <donmoir@comcast.net>.

libavdevice/dshow.c

@@ -45,13 +45,17 @@ struct dshow_ctx {
     libAVPin    *capture_pin[2];
 
     HANDLE mutex;
-    HANDLE event;
+    HANDLE event[2]; /* event[0] is set by DirectShow
+                      * event[1] is set by callback() */
     AVPacketList *pktl;
 
+    int eof;
+
     int64_t curbufsize;
     unsigned int video_frame_num;
 
     IMediaControl *control;
+    IMediaEvent *media_event;
 
     enum AVPixelFormat pixel_format;
     enum AVCodecID video_codec_id;
@@ -118,6 +122,9 @@ dshow_read_close(AVFormatContext *s)
         IMediaControl_Release(ctx->control);
     }
 
+    if (ctx->media_event)
+        IMediaEvent_Release(ctx->media_event);
+
     if (ctx->graph) {
         IEnumFilters *fenum;
         int r;
@@ -161,8 +168,10 @@ dshow_read_close(AVFormatContext *s)
 
     if(ctx->mutex)
         CloseHandle(ctx->mutex);
-    if(ctx->event)
+    if(ctx->event[0])
-        CloseHandle(ctx->event);
+        CloseHandle(ctx->event[0]);
+    if(ctx->event[1])
+        CloseHandle(ctx->event[1]);
 
     pktl = ctx->pktl;
     while (pktl) {
@@ -233,7 +242,7 @@ callback(void *priv_data, int index, uint8_t *buf, int buf_size, int64_t time)
 
     ctx->curbufsize += buf_size;
 
-    SetEvent(ctx->event);
+    SetEvent(ctx->event[1]);
     ReleaseMutex(ctx->mutex);
 
     return;
@@ -868,6 +877,9 @@ static int dshow_read_header(AVFormatContext *avctx)
     IGraphBuilder *graph = NULL;
     ICreateDevEnum *devenum = NULL;
     IMediaControl *control = NULL;
+    IMediaEvent *media_event = NULL;
+    HANDLE media_event_handle;
+    HANDLE proc;
     int ret = AVERROR(EIO);
     int r;
 
@@ -948,8 +960,8 @@ static int dshow_read_header(AVFormatContext *avctx)
         av_log(avctx, AV_LOG_ERROR, "Could not create Mutex\n");
         goto error;
     }
-    ctx->event = CreateEvent(NULL, 1, 0, NULL);
+    ctx->event[1] = CreateEvent(NULL, 1, 0, NULL);
-    if (!ctx->event) {
+    if (!ctx->event[1]) {
         av_log(avctx, AV_LOG_ERROR, "Could not create Event\n");
         goto error;
     }
@@ -961,6 +973,26 @@ static int dshow_read_header(AVFormatContext *avctx)
     }
     ctx->control = control;
 
+    r = IGraphBuilder_QueryInterface(graph, &IID_IMediaEvent, (void **) &media_event);
+    if (r != S_OK) {
+        av_log(avctx, AV_LOG_ERROR, "Could not get media event.\n");
+        goto error;
+    }
+    ctx->media_event = media_event;
+
+    r = IMediaEvent_GetEventHandle(media_event, (void *) &media_event_handle);
+    if (r != S_OK) {
+        av_log(avctx, AV_LOG_ERROR, "Could not get media event handle.\n");
+        goto error;
+    }
+    proc = GetCurrentProcess();
+    r = DuplicateHandle(proc, media_event_handle, proc, &ctx->event[0],
+                        0, 0, DUPLICATE_SAME_ACCESS);
+    if (!r) {
+        av_log(avctx, AV_LOG_ERROR, "Could not duplicate media event handle.\n");
+        goto error;
+    }
+
     r = IMediaControl_Run(control);
     if (r == S_FALSE) {
         OAFilterState pfs;
@@ -984,12 +1016,32 @@ error:
     return ret;
 }
 
+/**
+ * Checks media events from DirectShow and returns -1 on error or EOF. Also
+ * purges all events that might be in the event queue to stop the trigger
+ * of event notification.
+ */
+static int dshow_check_event_queue(IMediaEvent *media_event)
+{
+    LONG_PTR p1, p2;
+    long code;
+    int ret = 0;
+
+    while (IMediaEvent_GetEvent(media_event, &code, &p1, &p2, 0) != E_ABORT) {
+        if (code == EC_COMPLETE || code == EC_DEVICE_LOST || code == EC_ERRORABORT)
+            ret = -1;
+        IMediaEvent_FreeEventParams(media_event, code, p1, p2);
+    }
+
+    return ret;
+}
+
 static int dshow_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     struct dshow_ctx *ctx = s->priv_data;
     AVPacketList *pktl = NULL;
 
-    while (!pktl) {
+    while (!ctx->eof && !pktl) {
         WaitForSingleObject(ctx->mutex, INFINITE);
         pktl = ctx->pktl;
         if (pktl) {
@@ -998,18 +1050,20 @@ static int dshow_read_packet(AVFormatContext *s, AVPacket *pkt)
             av_free(pktl);
             ctx->curbufsize -= pkt->size;
         }
-        ResetEvent(ctx->event);
+        ResetEvent(ctx->event[1]);
         ReleaseMutex(ctx->mutex);
         if (!pktl) {
-            if (s->flags & AVFMT_FLAG_NONBLOCK) {
+            if (dshow_check_event_queue(ctx->media_event) < 0) {
+                ctx->eof = 1;
+            } else if (s->flags & AVFMT_FLAG_NONBLOCK) {
                 return AVERROR(EAGAIN);
             } else {
-                WaitForSingleObject(ctx->event, INFINITE);
+                WaitForMultipleObjects(2, ctx->event, 0, INFINITE);
             }
         }
     }
 
-    return pkt->size;
+    return ctx->eof ? AVERROR(EIO) : pkt->size;
 }
 
 #define OFFSET(x) offsetof(struct dshow_ctx, x)

libavdevice/dshow_capture.h

@@ -32,6 +32,11 @@
 #include <dshow.h>
 #include <dvdmedia.h>
 
+/* EC_DEVICE_LOST is not defined in MinGW dshow headers. */
+#ifndef EC_DEVICE_LOST
+#define EC_DEVICE_LOST 0x1f
+#endif
+
 long ff_copy_dshow_media_type(AM_MEDIA_TYPE *dst, const AM_MEDIA_TYPE *src);
 void ff_print_VIDEO_STREAM_CONFIG_CAPS(const VIDEO_STREAM_CONFIG_CAPS *caps);
 void ff_print_AUDIO_STREAM_CONFIG_CAPS(const AUDIO_STREAM_CONFIG_CAPS *caps);