From: Christian Gagneraud &lt;chris(a)techworks.ie&gt; gr-osmosdr uses the driver in a multi-thread context, as a side effect the cancel_async() can be called before read_async(), in such a case the cancel is "forgotten". This patch fixed that by being a bit more relaxed with state machine transitions. This patch doesn't fix any race conditions, it just make an anoying one less likely to happen. This patch goes along this one [1] [1] http://lists.osmocom.org/pipermail/osmocom-sdr/2012-August/000201.html Signed-off-by: Christian Gagneraud &lt;chris(a)techworks.ie&gt; --- src/librtlsdr.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/src/librtlsdr.c b/src/librtlsdr.c index 4e54d8e..d83010d 100644 --- a/src/librtlsdr.c +++ b/src/librtlsdr.c @@ -1256,6 +1256,12 @@ int rtlsdr_read_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, void *ctx, if (!dev) return -1; + /* It can happen if cancel_async is called before read_async */ + if (dev->async_status != RTLSDR_INACTIVE) + return -1; + + dev->async_status = RTLSDR_RUNNING; + dev->cb = cb; dev->cb_ctx = ctx; @@ -1284,8 +1290,6 @@ int rtlsdr_read_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, void *ctx, libusb_submit_transfer(dev->xfer[i]); } - dev->async_status = RTLSDR_RUNNING; - while (RTLSDR_INACTIVE != dev->async_status) { r = libusb_handle_events_timeout(dev->ctx, &tv); if (r < 0) { @@ -1326,7 +1330,7 @@ int rtlsdr_cancel_async(rtlsdr_dev_t *dev) if (!dev) return -1; - if (RTLSDR_RUNNING == dev->async_status) { + if (RTLSDR_CANCELING != dev->async_status) { dev->async_status = RTLSDR_CANCELING; return 0; } -- 1.7.7