[{"id":5231,"web_url":"https://patchwork.libcamera.org/comment/5231/","msgid":"<20200617010919.GS913@pendragon.ideasonboard.com>","date":"2020-06-17T01:09:19","subject":"Re: [libcamera-devel] [PATCH 11/15] v4l2: v4l2_camera: Don't use\n\tlibcamera::Semaphore for available buffers","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Paul,\n\nThank you for the patch.\n\nOn Tue, Jun 16, 2020 at 10:12:40PM +0900, Paul Elder wrote:\n> In V4L2, a blocked dqbuf should not not also block a streamoff. This\n> means that on streamoff, the blocked dqbuf must return (with error). We\n> cannot do this with the libcamera semaphore, so pull out the necessary\n> components of a semaphore, and put them into V4L2Camera, so that dqbuf\n> from V4L2CameraProxy can wait on a disjunct condition of the\n> availability of the semaphore or the stopping of the stream.\n> \n> Signed-off-by: Paul Elder \n> ---\n> src/v4l2/v4l2_camera.cpp | 32 ++++++++++++++++++++++++++++++--\n> src/v4l2/v4l2_camera.h | 8 +++++++-\n> src/v4l2/v4l2_camera_proxy.cpp | 11 +++++++++--\n> 3 files changed, 46 insertions(+), 5 deletions(-)\n> \n> diff --git a/src/v4l2/v4l2_camera.cpp b/src/v4l2/v4l2_camera.cpp\n> index fdbf461..f0ec54b 100644\n> --- a/src/v4l2/v4l2_camera.cpp\n> +++ b/src/v4l2/v4l2_camera.cpp\n> @@ -18,7 +18,7 @@ LOG_DECLARE_CATEGORY(V4L2Compat);\n> \n> V4L2Camera::V4L2Camera(std::shared_ptr camera)\n> \t: camera_(camera), isRunning_(false), bufferAllocator_(nullptr),\n> -\t efd_(-1)\n> +\t efd_(-1), bufferAvailableCount_(0)\n> {\n> \tcamera_->requestCompleted.connect(this, &V4L2Camera::requestComplete);\n> }\n> @@ -100,7 +100,9 @@ void V4L2Camera::requestComplete(Request *request)\n> \tif (ret != sizeof(data))\n> \t\tLOG(V4L2Compat, Error) << \"Failed to signal eventfd POLLIN\";\n> \n> -\tbufferSema_.release();\n> +\tMutexLocker locker(bufferMutex_);\n> +\tbufferAvailableCount_++;\n> +\tbufferCV_.notify_all();\n> }\n> \n> int V4L2Camera::configure(StreamConfiguration *streamConfigOut,\n> @@ -151,6 +153,7 @@ int V4L2Camera::allocBuffers(unsigned int count)\n> void V4L2Camera::freeBuffers()\n> {\n> \tStream *stream = *camera_->streams().begin();\n> +\n> \tbufferAllocator_->free(stream);\n> }\n> \n> @@ -168,6 +171,7 @@ FileDescriptor V4L2Camera::getBufferFd(unsigned int index)\n> \n> int V4L2Camera::streamOn()\n> {\n> +\tMutexLocker locker(isRunningMutex_);\n> \tif (isRunning_)\n> \t\treturn 0;\n> \n> @@ -191,6 +195,7 @@ int V4L2Camera::streamOn()\n> \n> int V4L2Camera::streamOff()\n> {\n> +\tMutexLocker locker(isRunningMutex_);\n> \t/* \\todo Restore buffers to reqbufs state? */\n> \tif (!isRunning_)\n> \t\treturn 0;\n> @@ -200,12 +205,15 @@ int V4L2Camera::streamOff()\n> \t\treturn ret == -EACCES ? -EBUSY : ret;\n> \n> \tisRunning_ = false;\n> +\tbufferCV_.notify_all();\n> \n> \treturn 0;\n> }\n> \n> int V4L2Camera::qbuf(unsigned int index)\n> {\n> +\tMutexLocker locker(isRunningMutex_);\n> +\n> \tstd::unique_ptr request =\n> \t\tstd::unique_ptr(camera_->createRequest(index));\n> \tif (!request) {\n> @@ -234,3 +242,23 @@ int V4L2Camera::qbuf(unsigned int index)\n> \n> \treturn 0;\n> }\n> +\n> +void V4L2Camera::waitForBufferAvailable()\n> +{\n> +\tMutexLocker locker(bufferMutex_);\n> +\tbufferCV_.wait(locker, [&] {\n> +\t\t\treturn bufferAvailableCount_ >= 1 || !isRunning_;\n> +\t\t\t});\n> +\tif (isRunning_)\n> +\t\tbufferAvailableCount_--;\n> +}\n> +\n> +bool V4L2Camera::isBufferAvailable()\n> +{\n> +\tMutexLocker locker(bufferMutex_);\n> +\tif (bufferAvailableCount_ < 1)\n> +\t\treturn false;\n> +\n> +\tbufferAvailableCount_--;\n> +\treturn true;\n> +}\n> diff --git a/src/v4l2/v4l2_camera.h b/src/v4l2/v4l2_camera.h\n> index 30114ed..81dcbe2 100644\n> --- a/src/v4l2/v4l2_camera.h\n> +++ b/src/v4l2/v4l2_camera.h\n> @@ -57,7 +57,8 @@ public:\n> \n> \tint qbuf(unsigned int index);\n> \n> -\tSemaphore bufferSema_;\n> +\tvoid waitForBufferAvailable();\n> +\tbool isBufferAvailable();\n> \n> private:\n> \tvoid requestComplete(Request *request);\n> @@ -65,6 +66,7 @@ private:\n> \tstd::shared_ptr camera_;\n> \tstd::unique_ptr config_;\n> \n> +\tMutex isRunningMutex_;\n\nWhy do you use a separate mutex for this, especially given that\nV4L2Camera::waitForBufferAvailable() accesses isRunning_ using\nbufferMutex_, not isRunningMutex_ ?\n\n> \tbool isRunning_;\n> \n> \tstd::mutex bufferLock_;\n> @@ -74,6 +76,10 @@ private:\n> \tstd::deque> completedBuffers_;\n> \n> \tint efd_;\n> +\n> +\tMutex bufferMutex_;\n> +\tstd::condition_variable bufferCV_;\n> +\tunsigned int bufferAvailableCount_;\n> };\n> \n> #endif /* __V4L2_CAMERA_H__ */\n> diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp\n> index 45e4656..079961a 100644\n> --- a/src/v4l2/v4l2_camera_proxy.cpp\n> +++ b/src/v4l2/v4l2_camera_proxy.cpp\n> @@ -648,10 +648,17 @@ int V4L2CameraProxy::vidioc_dqbuf(int fd, struct v4l2_buffer *arg)\n> \t\treturn -EINVAL;\n> \n> \tif (!nonBlockingFds_[fd])\n> -\t\tvcam_->bufferSema_.acquire();\n> -\telse if (!vcam_->bufferSema_.tryAcquire())\n> +\t\tvcam_->waitForBufferAvailable();\n> +\telse if (!vcam_->isBufferAvailable())\n> \t\treturn -EAGAIN;\n> \n> +\t/*\n> +\t * We need to check here again in case stream was turned off while we\n> +\t * were blocked on dqbuf.\n> +\t */\n> +\tif (!streaming_)\n> +\t\treturn -EINVAL;\n> +\n> \tupdateBuffers();\n> \n> \tstruct v4l2_buffer &buf = buffers_[currentBuf_];","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 733EE603D8\n\tfor ;\n\tWed, 17 Jun 2020 03:09:42 +0200 (CEST)","from pendragon.ideasonboard.com (81-175-216-236.bb.dnainternet.fi\n\t[81.175.216.236])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id EC5B1F9;\n\tWed, 17 Jun 2020 03:09:41 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key; \n\tunprotected) header.d=ideasonboard.com\n\theader.i=@ideasonboard.com\n\theader.b=\"PGKn+XZS\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1592356182;\n\tbh=8N0l0bhCslMNaQPne7VqHRsKAgVhZkyS85Bi69CGbeU=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=PGKn+XZSJb+v5knRewKdBWmKnbOuLy/+++BeRW/Fn3+ZgKCGjyLt2iDOsdKR4NNtX\n\t86v/zoJvnuCVlw+S2xOTjS3ojAUDgLtb2If0qQ3f+ej9PLn6gKlFBk2D3wXM290ipp\n\t5CCGQDQhgNF0/PAY//XznYGKBixyRq1ZgwDrY73Y=","Date":"Wed, 17 Jun 2020 04:09:19 +0300","From":"Laurent Pinchart ","To":"Paul Elder ","Cc":"libcamera-devel@lists.libcamera.org","Message-ID":"<20200617010919.GS913@pendragon.ideasonboard.com>","References":"<20200616131244.70308-1-paul.elder@ideasonboard.com>\n\t<20200616131244.70308-12-paul.elder@ideasonboard.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<20200616131244.70308-12-paul.elder@ideasonboard.com>","Subject":"Re: [libcamera-devel] [PATCH 11/15] v4l2: v4l2_camera: Don't use\n\tlibcamera::Semaphore for available buffers","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Wed, 17 Jun 2020 01:09:42 -0000"}}]