[{"id":2980,"web_url":"https://patchwork.libcamera.org/comment/2980/","msgid":"<20191028110657.GF20198@bigcity.dyn.berto.se>","date":"2019-10-28T11:06:57","subject":"Re: [libcamera-devel] [PATCH v2 1/9] libcamera: Add Semaphore class","submitter":{"id":5,"url":"https://patchwork.libcamera.org/api/people/5/","name":"Niklas Söderlund","email":"niklas.soderlund@ragnatech.se"},"content":"Hi Laurent,\n\nThanks for your patch.\n\nOn 2019-10-28 12:49:05 +0200, Laurent Pinchart wrote:\n> Add a general-purpose counting semaphore class.\n> \n> Signed-off-by: Laurent Pinchart \n\nReviewed-by: Niklas Söderlund \n\n> ---\n> src/libcamera/include/meson.build | 1 +\n> src/libcamera/include/semaphore.h | 34 ++++++++++\n> src/libcamera/meson.build | 1 +\n> src/libcamera/semaphore.cpp | 103 ++++++++++++++++++++++++++++++\n> 4 files changed, 139 insertions(+)\n> create mode 100644 src/libcamera/include/semaphore.h\n> create mode 100644 src/libcamera/semaphore.cpp\n> \n> diff --git a/src/libcamera/include/meson.build b/src/libcamera/include/meson.build\n> index 2c74d29bd925..64c2155f90cf 100644\n> --- a/src/libcamera/include/meson.build\n> +++ b/src/libcamera/include/meson.build\n> @@ -17,6 +17,7 @@ libcamera_headers = files([\n> 'message.h',\n> 'pipeline_handler.h',\n> 'process.h',\n> + 'semaphore.h',\n> 'thread.h',\n> 'utils.h',\n> 'v4l2_controls.h',\n> diff --git a/src/libcamera/include/semaphore.h b/src/libcamera/include/semaphore.h\n> new file mode 100644\n> index 000000000000..c6b286536eb3\n> --- /dev/null\n> +++ b/src/libcamera/include/semaphore.h\n> @@ -0,0 +1,34 @@\n> +/* SPDX-License-Identifier: LGPL-2.1-or-later */\n> +/*\n> + * Copyright (C) 2019, Google Inc.\n> + *\n> + * semaphore.h - General-purpose counting semaphore\n> + */\n> +#ifndef __LIBCAMERA_SEMAPHORE_H__\n> +#define __LIBCAMERA_SEMAPHORE_H__\n> +\n> +#include \n> +\n> +#include \"thread.h\"\n> +\n> +namespace libcamera {\n> +\n> +class Semaphore\n> +{\n> +public:\n> +\tSemaphore(unsigned int n = 0);\n> +\n> +\tunsigned int available();\n> +\tvoid acquire(unsigned int n = 1);\n> +\tbool tryAcquire(unsigned int n = 1);\n> +\tvoid release(unsigned int n = 1);\n> +\n> +private:\n> +\tMutex mutex_;\n> +\tstd::condition_variable cv_;\n> +\tunsigned int available_;\n> +};\n> +\n> +} /* namespace libcamera */\n> +\n> +#endif /* __LIBCAMERA_SEMAPHORE_H__ */\n> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build\n> index d329820b9582..dab5dbff77b7 100644\n> --- a/src/libcamera/meson.build\n> +++ b/src/libcamera/meson.build\n> @@ -27,6 +27,7 @@ libcamera_sources = files([\n> 'pipeline_handler.cpp',\n> 'process.cpp',\n> 'request.cpp',\n> + 'semaphore.cpp',\n> 'signal.cpp',\n> 'stream.cpp',\n> 'thread.cpp',\n> diff --git a/src/libcamera/semaphore.cpp b/src/libcamera/semaphore.cpp\n> new file mode 100644\n> index 000000000000..ce1eae4914ed\n> --- /dev/null\n> +++ b/src/libcamera/semaphore.cpp\n> @@ -0,0 +1,103 @@\n> +/* SPDX-License-Identifier: LGPL-2.1-or-later */\n> +/*\n> + * Copyright (C) 2019, Google Inc.\n> + *\n> + * semaphore.cpp - General-purpose counting semaphore\n> + */\n> +\n> +#include \"semaphore.h\"\n> +#include \"thread.h\"\n> +\n> +/**\n> + * \\file semaphore.h\n> + * \\brief General-purpose counting semaphore\n> + */\n> +\n> +namespace libcamera {\n> +\n> +/**\n> + * \\class Semaphore\n> + * \\brief General-purpose counting semaphore\n> + *\n> + * A semaphore is a locking primitive that protects resources. It is created\n> + * with an initial number of resources (which may be 0), and offers two\n> + * primitives to acquire and release resources. The acquire() method tries to\n> + * acquire a number of resources, and blocks if not enough resources are\n> + * available until they get released. The release() method releases a number of\n> + * resources, waking up any consumer blocked on an acquire() call.\n> + */\n> +\n> +/**\n> + * \\brief Construct a semaphore with \\a n resources\n> + * \\param[in] n The resource count\n> + */\n> +Semaphore::Semaphore(unsigned int n)\n> +\t: available_(n)\n> +{\n> +}\n> +\n> +/**\n> + * \\brief Retrieve the number of available resources\n> + * \\return The number of available resources\n> + */\n> +unsigned int Semaphore::available()\n> +{\n> +\tMutexLocker locker(mutex_);\n> +\treturn available_;\n> +}\n> +\n> +/**\n> + * \\brief Acquire \\a n resources\n> + * \\param[in] n The resource count\n> + *\n> + * This method attempts to acquire \\a n resources. If \\a n is higher than the\n> + * number of available resources, the call will block until enough resources\n> + * become available.\n> + */\n> +void Semaphore::acquire(unsigned int n)\n> +{\n> +\tMutexLocker locker(mutex_);\n> +\tcv_.wait(locker, [&] { return available_ >= n; });\n> +\tavailable_ -= n;\n> +}\n> +\n> +/**\n> + * \\brief Try to acquire \\a n resources without blocking\n> + * \\param[in] n The resource count\n> + *\n> + * This method attempts to acquire \\a n resources. If \\a n is higher than the\n> + * number of available resources, it returns false immediately without\n> + * acquiring any resource. Otherwise it acquires the resources and returns\n> + * true.\n> + *\n> + * \\return True if the resources have been acquired, false otherwise\n> + */\n> +bool Semaphore::tryAcquire(unsigned int n)\n> +{\n> +\tMutexLocker locker(mutex_);\n> +\tif (available_ < n)\n> +\t\treturn false;\n> +\n> +\tavailable_ -= n;\n> +\treturn true;\n> +}\n> +\n> +/**\n> + * \\brief Release \\a n resources\n> + * \\param[in] n The resource count\n> + *\n> + * This method releases \\a n resources, increasing the available resource count\n> + * by \\a n. If the number of available resources becomes large enough for any\n> + * consumer blocked on an acquire() call, those consumers get woken up.\n> + */\n> +void Semaphore::release(unsigned int n)\n> +{\n> +\t{\n> +\t\tMutexLocker locker(mutex_);\n> +\t\tavailable_ += n;\n> +\t}\n> +\n> +\tcv_.notify_all();\n> +}\n> +\n> +} /* namespace libcamera */\n> -- \n> Regards,\n> \n> Laurent Pinchart\n> \n> _______________________________________________\n> libcamera-devel mailing list\n> libcamera-devel@lists.libcamera.org\n> https://lists.libcamera.org/listinfo/libcamera-devel","headers":{"Return-Path":"","Received":["from mail-lj1-x241.google.com (mail-lj1-x241.google.com\n\t[IPv6:2a00:1450:4864:20::241])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 8A59260180\n\tfor ;\n\tMon, 28 Oct 2019 12:06:58 +0100 (CET)","by mail-lj1-x241.google.com with SMTP id q78so10848081lje.5\n\tfor ;\n\tMon, 28 Oct 2019 04:06:58 -0700 (PDT)","from localhost (h-93-159.A463.priv.bahnhof.se. 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