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80 lines
3.6 KiB
Markdown
80 lines
3.6 KiB
Markdown
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Weak-JACK
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=========
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This small library abstracts the [JACK](http://jackaudio.org) Application Binary Interface.
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Background and Motivation
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-------------------------
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The jack shared library needs to be installed system-wide (for all jack applications
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to share), it can not be part of an application itself.
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JACK developers take great care to not break binary compatibility of libjack. An
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application compiled with one version of jack will work with all future versions
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of jack. However, this only works well on GNU/Linux, BSD and to some extend on OSX.
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weak-jack linking is useful (at least) in the following cases:
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* the resulting application should not be directly linked to libjack.[so|dll|dylib]
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IOW: the application should start even if libjack is not installed.
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* the ABI of libjack is not stable. Note, this is only relevant for the Windows .dll
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(e.g. applications compiled and linked with jack-1.9.9 will crash with jack-1.9.10
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on windows. -- MSVC has a workaround: link by function-name, not ordinal, mingw
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does not offer this)
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* Reference new API functions (e.g. meta-data API or new latency compensation)
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in the application, which is not available on older versions of jack.
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Usage
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-----
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1. Copy the source files into your application's source (or use a git submodule)
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2. replace all `#include<jack/*>` in your sources with `#include "weak-jack.h"`
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3. add `weak_libjack.c` to the build-source of your project
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(in case your build-system does not detect `#include` dependencies automatically,
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also reference the header and .def file).
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4. Define `USE_WEAK_JACK` for all platforms where you want to use weak-linking. Usually
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`CFLAGS+=-DUSE_WEAK_JACK CXXFLAGS+=-DUSE_WEAK_JACK`
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5. Do not link your application to libjack (`-ljack`) when `USE_WEAK_JACK` is defined.
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Note the jack-headers still need to be present when compiling the application.
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The application code itself does not need to be changed.
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The first call to `jack_client_open()` will try to find and load libjack, if it cannot be
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found, it will fail (return `NULL` and set `jack_status_t` if provided to `JackFailure`.)
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It is possible to explicitly initialize and query availability of libjack using
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`have_libjack();` it returns 0 if libjack is available and can be used. (see the header
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file for non-zero error codes).
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Caveats
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-------
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If libjack is not available, all `jack_*` API calls are turned into no-operation functions.
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This is not a problem in general, as jack-applications will not use any part of the jack API if
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jack_client_open fails. The only exception here may be `jack_ringbuffer`. Note that the ringbuffer
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implementation is also part of libjack and will not be available.
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The dummy implementation for the ringbuffer API is safe (read, writes are ignored and return failure
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or zero-bytes length), but if your application depends on it to work, you're out of luck :)
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The function wrappers in `weak_libjack.def` were collected pragmatically it's quite possible that
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some JACK API calls have been missed. If you application fails to link (without -ljack), please report
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at https://github.com/x42/weakjack/issues
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License
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-------
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GNU General Public License version 2 (or later).
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Alternatives
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------------
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An alternative, more liberally licensed, implementation that abstracts and wraps jack completely
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(incl headers) can be found at
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https://github.com/falkTX/Carla/tree/master/source/jackbridge (C++ only),
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and a jack2 specific version at https://github.com/sletz/jack2/blob/master/common/JackWeakAPI.c
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A variant for python bindings is also provided by falkTX:
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https://github.com/falkTX/Cadence/blob/master/src/jacklib.py
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