First Commit

externals/openal-soft/alc/backends/jack.cpp

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+/**
+ * OpenAL cross platform audio library
+ * Copyright (C) 1999-2007 by authors.
+ * This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ *  License along with this library; if not, write to the
+ *  Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ * Or go to http://www.gnu.org/copyleft/lgpl.html
+ */
+
+#include "config.h"
+
+#include "jack.h"
+
+#include <cstdlib>
+#include <cstdio>
+#include <cstring>
+#include <memory.h>
+
+#include <array>
+#include <thread>
+#include <functional>
+
+#include "alc/alconfig.h"
+#include "alnumeric.h"
+#include "core/device.h"
+#include "core/helpers.h"
+#include "core/logging.h"
+#include "dynload.h"
+#include "ringbuffer.h"
+#include "threads.h"
+
+#include <jack/jack.h>
+#include <jack/ringbuffer.h>
+
+
+namespace {
+
+#ifdef HAVE_DYNLOAD
+#define JACK_FUNCS(MAGIC)          \
+    MAGIC(jack_client_open);       \
+    MAGIC(jack_client_close);      \
+    MAGIC(jack_client_name_size);  \
+    MAGIC(jack_get_client_name);   \
+    MAGIC(jack_connect);           \
+    MAGIC(jack_activate);          \
+    MAGIC(jack_deactivate);        \
+    MAGIC(jack_port_register);     \
+    MAGIC(jack_port_unregister);   \
+    MAGIC(jack_port_get_buffer);   \
+    MAGIC(jack_port_name);         \
+    MAGIC(jack_get_ports);         \
+    MAGIC(jack_free);              \
+    MAGIC(jack_get_sample_rate);   \
+    MAGIC(jack_set_error_function); \
+    MAGIC(jack_set_process_callback); \
+    MAGIC(jack_set_buffer_size_callback); \
+    MAGIC(jack_set_buffer_size);   \
+    MAGIC(jack_get_buffer_size);
+
+void *jack_handle;
+#define MAKE_FUNC(f) decltype(f) * p##f
+JACK_FUNCS(MAKE_FUNC)
+decltype(jack_error_callback) * pjack_error_callback;
+#undef MAKE_FUNC
+
+#ifndef IN_IDE_PARSER
+#define jack_client_open pjack_client_open
+#define jack_client_close pjack_client_close
+#define jack_client_name_size pjack_client_name_size
+#define jack_get_client_name pjack_get_client_name
+#define jack_connect pjack_connect
+#define jack_activate pjack_activate
+#define jack_deactivate pjack_deactivate
+#define jack_port_register pjack_port_register
+#define jack_port_unregister pjack_port_unregister
+#define jack_port_get_buffer pjack_port_get_buffer
+#define jack_port_name pjack_port_name
+#define jack_get_ports pjack_get_ports
+#define jack_free pjack_free
+#define jack_get_sample_rate pjack_get_sample_rate
+#define jack_set_error_function pjack_set_error_function
+#define jack_set_process_callback pjack_set_process_callback
+#define jack_set_buffer_size_callback pjack_set_buffer_size_callback
+#define jack_set_buffer_size pjack_set_buffer_size
+#define jack_get_buffer_size pjack_get_buffer_size
+#define jack_error_callback (*pjack_error_callback)
+#endif
+#endif
+
+
+constexpr char JackDefaultAudioType[] = JACK_DEFAULT_AUDIO_TYPE;
+
+jack_options_t ClientOptions = JackNullOption;
+
+bool jack_load()
+{
+    bool error{false};
+
+#ifdef HAVE_DYNLOAD
+    if(!jack_handle)
+    {
+        std::string missing_funcs;
+
+#ifdef _WIN32
+#define JACKLIB "libjack.dll"
+#else
+#define JACKLIB "libjack.so.0"
+#endif
+        jack_handle = LoadLib(JACKLIB);
+        if(!jack_handle)
+        {
+            WARN("Failed to load %s\n", JACKLIB);
+            return false;
+        }
+
+        error = false;
+#define LOAD_FUNC(f) do {                                                     \
+    p##f = reinterpret_cast<decltype(p##f)>(GetSymbol(jack_handle, #f));      \
+    if(p##f == nullptr) {                                                     \
+        error = true;                                                         \
+        missing_funcs += "\n" #f;                                             \
+    }                                                                         \
+} while(0)
+        JACK_FUNCS(LOAD_FUNC);
+#undef LOAD_FUNC
+        /* Optional symbols. These don't exist in all versions of JACK. */
+#define LOAD_SYM(f) p##f = reinterpret_cast<decltype(p##f)>(GetSymbol(jack_handle, #f))
+        LOAD_SYM(jack_error_callback);
+#undef LOAD_SYM
+
+        if(error)
+        {
+            WARN("Missing expected functions:%s\n", missing_funcs.c_str());
+            CloseLib(jack_handle);
+            jack_handle = nullptr;
+        }
+    }
+#endif
+
+    return !error;
+}
+
+
+struct JackDeleter {
+    void operator()(void *ptr) { jack_free(ptr); }
+};
+using JackPortsPtr = std::unique_ptr<const char*[],JackDeleter>;
+
+struct DeviceEntry {
+    std::string mName;
+    std::string mPattern;
+
+    template<typename T, typename U>
+    DeviceEntry(T&& name, U&& pattern)
+        : mName{std::forward<T>(name)}, mPattern{std::forward<U>(pattern)}
+    { }
+};
+
+al::vector<DeviceEntry> PlaybackList;
+
+
+void EnumerateDevices(jack_client_t *client, al::vector<DeviceEntry> &list)
+{
+    std::remove_reference_t<decltype(list)>{}.swap(list);
+
+    if(JackPortsPtr ports{jack_get_ports(client, nullptr, JackDefaultAudioType, JackPortIsInput)})
+    {
+        for(size_t i{0};ports[i];++i)
+        {
+            const char *sep{std::strchr(ports[i], ':')};
+            if(!sep || ports[i] == sep) continue;
+
+            const al::span<const char> portdev{ports[i], sep};
+            auto check_name = [portdev](const DeviceEntry &entry) -> bool
+            {
+                const size_t len{portdev.size()};
+                return entry.mName.length() == len
+                    && entry.mName.compare(0, len, portdev.data(), len) == 0;
+            };
+            if(std::find_if(list.cbegin(), list.cend(), check_name) != list.cend())
+                continue;
+
+            std::string name{portdev.data(), portdev.size()};
+            list.emplace_back(name, name+":");
+            const auto &entry = list.back();
+            TRACE("Got device: %s = %s\n", entry.mName.c_str(), entry.mPattern.c_str());
+        }
+        /* There are ports but couldn't get device names from them. Add a
+         * generic entry.
+         */
+        if(ports[0] && list.empty())
+        {
+            WARN("No device names found in available ports, adding a generic name.\n");
+            list.emplace_back("JACK", "");
+        }
+    }
+
+    if(auto listopt = ConfigValueStr(nullptr, "jack", "custom-devices"))
+    {
+        for(size_t strpos{0};strpos < listopt->size();)
+        {
+            size_t nextpos{listopt->find(';', strpos)};
+            size_t seppos{listopt->find('=', strpos)};
+            if(seppos >= nextpos || seppos == strpos)
+            {
+                const std::string entry{listopt->substr(strpos, nextpos-strpos)};
+                ERR("Invalid device entry: \"%s\"\n", entry.c_str());
+                if(nextpos != std::string::npos) ++nextpos;
+                strpos = nextpos;
+                continue;
+            }
+
+            const al::span<const char> name{listopt->data()+strpos, seppos-strpos};
+            const al::span<const char> pattern{listopt->data()+(seppos+1),
+                std::min(nextpos, listopt->size())-(seppos+1)};
+
+            /* Check if this custom pattern already exists in the list. */
+            auto check_pattern = [pattern](const DeviceEntry &entry) -> bool
+            {
+                const size_t len{pattern.size()};
+                return entry.mPattern.length() == len
+                    && entry.mPattern.compare(0, len, pattern.data(), len) == 0;
+            };
+            auto itemmatch = std::find_if(list.begin(), list.end(), check_pattern);
+            if(itemmatch != list.end())
+            {
+                /* If so, replace the name with this custom one. */
+                itemmatch->mName.assign(name.data(), name.size());
+                TRACE("Customized device name: %s = %s\n", itemmatch->mName.c_str(),
+                    itemmatch->mPattern.c_str());
+            }
+            else
+            {
+                /* Otherwise, add a new device entry. */
+                list.emplace_back(std::string{name.data(), name.size()},
+                    std::string{pattern.data(), pattern.size()});
+                const auto &entry = list.back();
+                TRACE("Got custom device: %s = %s\n", entry.mName.c_str(), entry.mPattern.c_str());
+            }
+
+            if(nextpos != std::string::npos) ++nextpos;
+            strpos = nextpos;
+        }
+    }
+
+    if(list.size() > 1)
+    {
+        /* Rename entries that have matching names, by appending '#2', '#3',
+         * etc, as needed.
+         */
+        for(auto curitem = list.begin()+1;curitem != list.end();++curitem)
+        {
+            auto check_match = [curitem](const DeviceEntry &entry) -> bool
+            { return entry.mName == curitem->mName; };
+            if(std::find_if(list.begin(), curitem, check_match) != curitem)
+            {
+                std::string name{curitem->mName};
+                size_t count{1};
+                auto check_name = [&name](const DeviceEntry &entry) -> bool
+                { return entry.mName == name; };
+                do {
+                    name = curitem->mName;
+                    name += " #";
+                    name += std::to_string(++count);
+                } while(std::find_if(list.begin(), curitem, check_name) != curitem);
+                curitem->mName = std::move(name);
+            }
+        }
+    }
+}
+
+
+struct JackPlayback final : public BackendBase {
+    JackPlayback(DeviceBase *device) noexcept : BackendBase{device} { }
+    ~JackPlayback() override;
+
+    int processRt(jack_nframes_t numframes) noexcept;
+    static int processRtC(jack_nframes_t numframes, void *arg) noexcept
+    { return static_cast<JackPlayback*>(arg)->processRt(numframes); }
+
+    int process(jack_nframes_t numframes) noexcept;
+    static int processC(jack_nframes_t numframes, void *arg) noexcept
+    { return static_cast<JackPlayback*>(arg)->process(numframes); }
+
+    int mixerProc();
+
+    void open(const char *name) override;
+    bool reset() override;
+    void start() override;
+    void stop() override;
+    ClockLatency getClockLatency() override;
+
+    std::string mPortPattern;
+
+    jack_client_t *mClient{nullptr};
+    std::array<jack_port_t*,MAX_OUTPUT_CHANNELS> mPort{};
+
+    std::mutex mMutex;
+
+    std::atomic<bool> mPlaying{false};
+    bool mRTMixing{false};
+    RingBufferPtr mRing;
+    al::semaphore mSem;
+
+    std::atomic<bool> mKillNow{true};
+    std::thread mThread;
+
+    DEF_NEWDEL(JackPlayback)
+};
+
+JackPlayback::~JackPlayback()
+{
+    if(!mClient)
+        return;
+
+    auto unregister_port = [this](jack_port_t *port) -> void
+    { if(port) jack_port_unregister(mClient, port); };
+    std::for_each(mPort.begin(), mPort.end(), unregister_port);
+    mPort.fill(nullptr);
+
+    jack_client_close(mClient);
+    mClient = nullptr;
+}
+
+
+int JackPlayback::processRt(jack_nframes_t numframes) noexcept
+{
+    std::array<jack_default_audio_sample_t*,MAX_OUTPUT_CHANNELS> out;
+    size_t numchans{0};
+    for(auto port : mPort)
+    {
+        if(!port || numchans == mDevice->RealOut.Buffer.size())
+            break;
+        out[numchans++] = static_cast<float*>(jack_port_get_buffer(port, numframes));
+    }
+
+    if(mPlaying.load(std::memory_order_acquire)) LIKELY
+        mDevice->renderSamples({out.data(), numchans}, static_cast<uint>(numframes));
+    else
+    {
+        auto clear_buf = [numframes](float *outbuf) -> void
+        { std::fill_n(outbuf, numframes, 0.0f); };
+        std::for_each(out.begin(), out.begin()+numchans, clear_buf);
+    }
+
+    return 0;
+}
+
+
+int JackPlayback::process(jack_nframes_t numframes) noexcept
+{
+    std::array<jack_default_audio_sample_t*,MAX_OUTPUT_CHANNELS> out;
+    size_t numchans{0};
+    for(auto port : mPort)
+    {
+        if(!port) break;
+        out[numchans++] = static_cast<float*>(jack_port_get_buffer(port, numframes));
+    }
+
+    jack_nframes_t total{0};
+    if(mPlaying.load(std::memory_order_acquire)) LIKELY
+    {
+        auto data = mRing->getReadVector();
+        jack_nframes_t todo{minu(numframes, static_cast<uint>(data.first.len))};
+        auto write_first = [&data,numchans,todo](float *outbuf) -> float*
+        {
+            const float *RESTRICT in = reinterpret_cast<float*>(data.first.buf);
+            auto deinterlace_input = [&in,numchans]() noexcept -> float
+            {
+                float ret{*in};
+                in += numchans;
+                return ret;
+            };
+            std::generate_n(outbuf, todo, deinterlace_input);
+            data.first.buf += sizeof(float);
+            return outbuf + todo;
+        };
+        std::transform(out.begin(), out.begin()+numchans, out.begin(), write_first);
+        total += todo;
+
+        todo = minu(numframes-total, static_cast<uint>(data.second.len));
+        if(todo > 0)
+        {
+            auto write_second = [&data,numchans,todo](float *outbuf) -> float*
+            {
+                const float *RESTRICT in = reinterpret_cast<float*>(data.second.buf);
+                auto deinterlace_input = [&in,numchans]() noexcept -> float
+                {
+                    float ret{*in};
+                    in += numchans;
+                    return ret;
+                };
+                std::generate_n(outbuf, todo, deinterlace_input);
+                data.second.buf += sizeof(float);
+                return outbuf + todo;
+            };
+            std::transform(out.begin(), out.begin()+numchans, out.begin(), write_second);
+            total += todo;
+        }
+
+        mRing->readAdvance(total);
+        mSem.post();
+    }
+
+    if(numframes > total)
+    {
+        const jack_nframes_t todo{numframes - total};
+        auto clear_buf = [todo](float *outbuf) -> void { std::fill_n(outbuf, todo, 0.0f); };
+        std::for_each(out.begin(), out.begin()+numchans, clear_buf);
+    }
+
+    return 0;
+}
+
+int JackPlayback::mixerProc()
+{
+    SetRTPriority();
+    althrd_setname(MIXER_THREAD_NAME);
+
+    const size_t frame_step{mDevice->channelsFromFmt()};
+
+    while(!mKillNow.load(std::memory_order_acquire)
+        && mDevice->Connected.load(std::memory_order_acquire))
+    {
+        if(mRing->writeSpace() < mDevice->UpdateSize)
+        {
+            mSem.wait();
+            continue;
+        }
+
+        auto data = mRing->getWriteVector();
+        size_t todo{data.first.len + data.second.len};
+        todo -= todo%mDevice->UpdateSize;
+
+        const auto len1 = static_cast<uint>(minz(data.first.len, todo));
+        const auto len2 = static_cast<uint>(minz(data.second.len, todo-len1));
+
+        std::lock_guard<std::mutex> _{mMutex};
+        mDevice->renderSamples(data.first.buf, len1, frame_step);
+        if(len2 > 0)
+            mDevice->renderSamples(data.second.buf, len2, frame_step);
+        mRing->writeAdvance(todo);
+    }
+
+    return 0;
+}
+
+
+void JackPlayback::open(const char *name)
+{
+    if(!mClient)
+    {
+        const PathNamePair &binname = GetProcBinary();
+        const char *client_name{binname.fname.empty() ? "alsoft" : binname.fname.c_str()};
+
+        jack_status_t status;
+        mClient = jack_client_open(client_name, ClientOptions, &status, nullptr);
+        if(mClient == nullptr)
+            throw al::backend_exception{al::backend_error::DeviceError,
+                "Failed to open client connection: 0x%02x", status};
+        if((status&JackServerStarted))
+            TRACE("JACK server started\n");
+        if((status&JackNameNotUnique))
+        {
+            client_name = jack_get_client_name(mClient);
+            TRACE("Client name not unique, got '%s' instead\n", client_name);
+        }
+    }
+
+    if(PlaybackList.empty())
+        EnumerateDevices(mClient, PlaybackList);
+
+    if(!name && !PlaybackList.empty())
+    {
+        name = PlaybackList[0].mName.c_str();
+        mPortPattern = PlaybackList[0].mPattern;
+    }
+    else
+    {
+        auto check_name = [name](const DeviceEntry &entry) -> bool
+        { return entry.mName == name; };
+        auto iter = std::find_if(PlaybackList.cbegin(), PlaybackList.cend(), check_name);
+        if(iter == PlaybackList.cend())
+            throw al::backend_exception{al::backend_error::NoDevice,
+                "Device name \"%s\" not found", name?name:""};
+        mPortPattern = iter->mPattern;
+    }
+
+    mRTMixing = GetConfigValueBool(name, "jack", "rt-mix", true);
+    jack_set_process_callback(mClient,
+        mRTMixing ? &JackPlayback::processRtC : &JackPlayback::processC, this);
+
+    mDevice->DeviceName = name;
+}
+
+bool JackPlayback::reset()
+{
+    auto unregister_port = [this](jack_port_t *port) -> void
+    { if(port) jack_port_unregister(mClient, port); };
+    std::for_each(mPort.begin(), mPort.end(), unregister_port);
+    mPort.fill(nullptr);
+
+    /* Ignore the requested buffer metrics and just keep one JACK-sized buffer
+     * ready for when requested.
+     */
+    mDevice->Frequency = jack_get_sample_rate(mClient);
+    mDevice->UpdateSize = jack_get_buffer_size(mClient);
+    if(mRTMixing)
+    {
+        /* Assume only two periods when directly mixing. Should try to query
+         * the total port latency when connected.
+         */
+        mDevice->BufferSize = mDevice->UpdateSize * 2;
+    }
+    else
+    {
+        const char *devname{mDevice->DeviceName.c_str()};
+        uint bufsize{ConfigValueUInt(devname, "jack", "buffer-size").value_or(mDevice->UpdateSize)};
+        bufsize = maxu(NextPowerOf2(bufsize), mDevice->UpdateSize);
+        mDevice->BufferSize = bufsize + mDevice->UpdateSize;
+    }
+
+    /* Force 32-bit float output. */
+    mDevice->FmtType = DevFmtFloat;
+
+    int port_num{0};
+    auto ports_end = mPort.begin() + mDevice->channelsFromFmt();
+    auto bad_port = mPort.begin();
+    while(bad_port != ports_end)
+    {
+        std::string name{"channel_" + std::to_string(++port_num)};
+        *bad_port = jack_port_register(mClient, name.c_str(), JackDefaultAudioType,
+            JackPortIsOutput | JackPortIsTerminal, 0);
+        if(!*bad_port) break;
+        ++bad_port;
+    }
+    if(bad_port != ports_end)
+    {
+        ERR("Failed to register enough JACK ports for %s output\n",
+            DevFmtChannelsString(mDevice->FmtChans));
+        if(bad_port == mPort.begin()) return false;
+
+        if(bad_port == mPort.begin()+1)
+            mDevice->FmtChans = DevFmtMono;
+        else
+        {
+            ports_end = mPort.begin()+2;
+            while(bad_port != ports_end)
+            {
+                jack_port_unregister(mClient, *(--bad_port));
+                *bad_port = nullptr;
+            }
+            mDevice->FmtChans = DevFmtStereo;
+        }
+    }
+
+    setDefaultChannelOrder();
+
+    return true;
+}
+
+void JackPlayback::start()
+{
+    if(jack_activate(mClient))
+        throw al::backend_exception{al::backend_error::DeviceError, "Failed to activate client"};
+
+    const char *devname{mDevice->DeviceName.c_str()};
+    if(ConfigValueBool(devname, "jack", "connect-ports").value_or(true))
+    {
+        JackPortsPtr pnames{jack_get_ports(mClient, mPortPattern.c_str(), JackDefaultAudioType,
+            JackPortIsInput)};
+        if(!pnames)
+        {
+            jack_deactivate(mClient);
+            throw al::backend_exception{al::backend_error::DeviceError, "No playback ports found"};
+        }
+
+        for(size_t i{0};i < al::size(mPort) && mPort[i];++i)
+        {
+            if(!pnames[i])
+            {
+                ERR("No physical playback port for \"%s\"\n", jack_port_name(mPort[i]));
+                break;
+            }
+            if(jack_connect(mClient, jack_port_name(mPort[i]), pnames[i]))
+                ERR("Failed to connect output port \"%s\" to \"%s\"\n", jack_port_name(mPort[i]),
+                    pnames[i]);
+        }
+    }
+
+    /* Reconfigure buffer metrics in case the server changed it since the reset
+     * (it won't change again after jack_activate), then allocate the ring
+     * buffer with the appropriate size.
+     */
+    mDevice->Frequency = jack_get_sample_rate(mClient);
+    mDevice->UpdateSize = jack_get_buffer_size(mClient);
+    mDevice->BufferSize = mDevice->UpdateSize * 2;
+
+    mRing = nullptr;
+    if(mRTMixing)
+        mPlaying.store(true, std::memory_order_release);
+    else
+    {
+        uint bufsize{ConfigValueUInt(devname, "jack", "buffer-size").value_or(mDevice->UpdateSize)};
+        bufsize = maxu(NextPowerOf2(bufsize), mDevice->UpdateSize);
+        mDevice->BufferSize = bufsize + mDevice->UpdateSize;
+
+        mRing = RingBuffer::Create(bufsize, mDevice->frameSizeFromFmt(), true);
+
+        try {
+            mPlaying.store(true, std::memory_order_release);
+            mKillNow.store(false, std::memory_order_release);
+            mThread = std::thread{std::mem_fn(&JackPlayback::mixerProc), this};
+        }
+        catch(std::exception& e) {
+            jack_deactivate(mClient);
+            mPlaying.store(false, std::memory_order_release);
+            throw al::backend_exception{al::backend_error::DeviceError,
+                "Failed to start mixing thread: %s", e.what()};
+        }
+    }
+}
+
+void JackPlayback::stop()
+{
+    if(mPlaying.load(std::memory_order_acquire))
+    {
+        mKillNow.store(true, std::memory_order_release);
+        if(mThread.joinable())
+        {
+            mSem.post();
+            mThread.join();
+        }
+
+        jack_deactivate(mClient);
+        mPlaying.store(false, std::memory_order_release);
+    }
+}
+
+
+ClockLatency JackPlayback::getClockLatency()
+{
+    ClockLatency ret;
+
+    std::lock_guard<std::mutex> _{mMutex};
+    ret.ClockTime = GetDeviceClockTime(mDevice);
+    ret.Latency  = std::chrono::seconds{mRing ? mRing->readSpace() : mDevice->UpdateSize};
+    ret.Latency /= mDevice->Frequency;
+
+    return ret;
+}
+
+
+void jack_msg_handler(const char *message)
+{
+    WARN("%s\n", message);
+}
+
+} // namespace
+
+bool JackBackendFactory::init()
+{
+    if(!jack_load())
+        return false;
+
+    if(!GetConfigValueBool(nullptr, "jack", "spawn-server", false))
+        ClientOptions = static_cast<jack_options_t>(ClientOptions | JackNoStartServer);
+
+    const PathNamePair &binname = GetProcBinary();
+    const char *client_name{binname.fname.empty() ? "alsoft" : binname.fname.c_str()};
+
+    void (*old_error_cb)(const char*){&jack_error_callback ? jack_error_callback : nullptr};
+    jack_set_error_function(jack_msg_handler);
+    jack_status_t status;
+    jack_client_t *client{jack_client_open(client_name, ClientOptions, &status, nullptr)};
+    jack_set_error_function(old_error_cb);
+    if(!client)
+    {
+        WARN("jack_client_open() failed, 0x%02x\n", status);
+        if((status&JackServerFailed) && !(ClientOptions&JackNoStartServer))
+            ERR("Unable to connect to JACK server\n");
+        return false;
+    }
+
+    jack_client_close(client);
+    return true;
+}
+
+bool JackBackendFactory::querySupport(BackendType type)
+{ return (type == BackendType::Playback); }
+
+std::string JackBackendFactory::probe(BackendType type)
+{
+    std::string outnames;
+    auto append_name = [&outnames](const DeviceEntry &entry) -> void
+    {
+        /* Includes null char. */
+        outnames.append(entry.mName.c_str(), entry.mName.length()+1);
+    };
+
+    const PathNamePair &binname = GetProcBinary();
+    const char *client_name{binname.fname.empty() ? "alsoft" : binname.fname.c_str()};
+    jack_status_t status;
+    switch(type)
+    {
+    case BackendType::Playback:
+        if(jack_client_t *client{jack_client_open(client_name, ClientOptions, &status, nullptr)})
+        {
+            EnumerateDevices(client, PlaybackList);
+            jack_client_close(client);
+        }
+        else
+            WARN("jack_client_open() failed, 0x%02x\n", status);
+        std::for_each(PlaybackList.cbegin(), PlaybackList.cend(), append_name);
+        break;
+    case BackendType::Capture:
+        break;
+    }
+    return outnames;
+}
+
+BackendPtr JackBackendFactory::createBackend(DeviceBase *device, BackendType type)
+{
+    if(type == BackendType::Playback)
+        return BackendPtr{new JackPlayback{device}};
+    return nullptr;
+}
+
+BackendFactory &JackBackendFactory::getFactory()
+{
+    static JackBackendFactory factory{};
+    return factory;
+}