Shared library data share

Audio Plugins
1

Hi, now a days i research for shared library.

i know audio plugin is shared library.

so i make 2 plugins, and 1 shared library(not audio)

so i shared data(variable int, float, array) between plugin using shared library.

i realize plugin1, 2 has different value.

if plugin 1 write (a =3)
then plugin 2 read a =0 ( i think ‘a’ in plugin2 has different memory address)

so any compile option(link option, such as symbol) is exist help me??

2

It depends on how you load the shared library. You probably want to use the dlopen command directly with the RTLD_GLOBAL flag. The default is that every plug-in which loads the shared library will have it’s own private copy.

3

thank you for your reply!
Actually, I also research before.
my plugins are opened by DAW(dopen dynamicallay), but my shared library is opened at first.

so in this case, i also adjust RTLD_GLOBAL? this means i give option at first.

4

Well it’s loading it before as you’ve linked your plug-in to the shared lib. Then you have no control over RTLD_GLOBAL. You need to not link you plug-in to the shared lib and resolve all symbols at run-time. This might be quite difficult to do. IMHO if you have no good reason to be loading a shared lib in your plug-in then you should probably avoid it. It can cause all sort of problems. For JUCE 4.1, we also put some of the JUCE code in a shared library. A storm of complaints and bugs came in via the forum so we reverted that change only a day later.

5

Thank you fabian.
and your experience about shared library in JUCE 4.1. (it is amazing)

so, shared memory (ipc, despite of same process) is the right access? (i also try - it works well)

ps. juce is amazing and i learn many things about audio programming and c++. thank you again.

6

Technically you could just use global variables as most hosts will only ever load your shared library once and then simply create several instances of your plug-in. Therefore, there will only be a single instance of your globals regardless of the number of plug-in instances loaded.

However, I personally would not rely on this behaviour. Some DAWs may sandbox plug-ins in the future and break your plug-in. I’d rather rely on IPC.