[swift-users] Communicating with dynamically loaded swift library

[Geordie Jay]

I think SwiftPM is (incorrectly) compiling A.XYZ into each of the modules
that depend on it, as well as into your intended libA.so file.

Try to ensure the plugin provider module (libA) is (only) being compiled
into its standalone shared library file. Try cleaning the swiftpm build for
one (swift package clean) and ensure the Package.swift files are correctly
set up to output the shared library.

Sorry I can’t be more specific, I’ve had these same kinds of issues before
but I’m not 100% what they were.

Geordie


Ján Kosa via swift-users <swift-users at swift.org> schrieb am Fr. 6. Okt.
2017 um 14:41:

> It worked! Took me a while to iron out details, but it is working now.
> Huge thanks sir, I will name my firstborn after you.
> Thanks for the @_cdecl("initializePlugin") tip as well, I didn't know
> about it and it will be very useful.
>
> I am having slightly related problem now (it was there before, but I
> ignored it for the time being), not sure if I should start a new thread?
>
> The PluginInterface module has one external dependency on module A,
> PluginConsumer has the dependency on module B which has dependency on same
> module A that the PluginInterface uses. When I load the plugin library, I
> get bunch of errors like:
>
> Class A.XYZ is implemented in both libPluginInterface.dylib and
> libMyPlugin.dylib
>
> I know why it is there, but I don't know how to get rid of it. I can't
> just remove dependency from PluginConsumer and use the one from
> PluginInterface (if that would even work?) because PluginConsumer does not
> depend on it directly, but it is going through module B first
>
> Cheers,
> Lope
>
> On 4 October 2017 at 22:17, Daniel Dunbar <daniel_dunbar at apple.com> wrote:
>
>> The way that I have done this in the past is pass a protocol as an unsafe
>> pointer to an exposed entry point:
>> ```swift
>>             let entryPoint = dlsym(handle, “initializePlugin”)
>>             guard entryPoint != nil else {
>>                 fatalError("missing plugin entry point: \(pluginPath)")
>>             }
>>             typealias PluginInitializationFunc = @convention(c)
>> (UnsafeRawPointer) -> ()
>>             let f = unsafeBitCast(entryPoint, to:
>> PluginInitializationFunc.self)
>>             f(Unmanaged.passUnretained(self).toOpaque())
>> ```
>>
>> and then in the plugin convert back to the appropriate type:
>>
>> ```
>> @_cdecl("initializePlugin")
>> public func initializePlugin(_ ptr: UnsafeRawPointer) {
>>     let manager =
>> Unmanaged<PluginManager>.fromOpaque(ptr).takeUnretainedValue()
>> ```
>>
>> HTH,
>>  - Daniel
>>
>> On Oct 4, 2017, at 11:02 AM, Ján Kosa via swift-users <
>> swift-users at swift.org> wrote:
>>
>> Hello folks,
>>
>> I have been toying with dynamic libraries, trying to implement plugin
>> functionality. I was able to get to the point where I can call simple
>> function in loaded library, but I am having troubles starting more
>> sophisticated communication channel.
>>
>> There are 3 projects
>> - PluginConsumer is an app that loads plugin libraries
>> - MyPlugin is a plugin implementation, output is dynamic library that
>> PluginConsumer loads
>> - PluginInterface is common interface that both MyPlugin and
>> PluginConsumer use, so that they know how to communicate
>>
>> My first idea was to have PluginInterface be a simple SPM project with
>> single file where the bare-bones PluginInterface class would be:
>>
>>
>> open class PluginInterface {
>>
>>     open func sayHi()
>>
>> }
>>
>>
>> Package.swift file:
>>
>>
>> // swift-tools-version:4.0
>>
>> import PackageDescription
>>
>> let package = Package(
>>
>>     name: "PluginInterface",
>>
>>     products: [ .library(name: "PluginInterface", type: .dynamic,
>> targets: ["PluginInterface"]) ],
>>
>>     targets: [ .target(name: "PluginInterface") ]
>>
>> )
>>
>>
>>
>> UserPlugin is also very simple project containing only one file:
>>
>>
>> public func getPlugin() -> AnyObject {
>>
>>     return MyPlugin()
>>
>> }
>>
>>
>> class MyPlugin: PluginInterface {
>>
>>     override func sayHi() {
>>
>>         print("Hi from my plugin")
>>
>>     }
>>
>> }
>>
>> Package.swift:
>>
>>
>> // swift-tools-version:4.0
>>
>> import PackageDescription
>>
>> let package = Package(
>>
>>     name: "MyPlugin",
>>
>>     products: [ .library(name: "MyPlugin", type: .dynamic, targets: [
>> "MyPlugin"]) ],
>>
>>     dependencies: [ .package(url: "url_to_PluginInterface", from: "0.0.0"),
>> ],
>>
>>     targets: [
>>
>>         .target(name: "PluginInterface", dependencies: ["PluginInterface"
>> ]),
>>
>>         .target(name: "MyPlugin", dependencies: ["PluginInterface"]),
>>
>>     ]
>>
>> )
>>
>>
>> The PluginConsumer is bit more complicated, but here is relevant part
>> (lib loading and function calling):
>>
>>
>> typealias InitFunction = @convention(c) () -> AnyObject
>>
>>
>> let openRes = dlopen(pathToLib, RTLD_NOW|RTLD_LOCAL)
>>
>> if openRes != nil {
>>
>>     defer {
>>
>>         dlclose(openRes)
>>
>>     }
>>
>>     let symbolName = "mangled_symbol_name"
>>
>>     let sym = dlsym(openRes, symbolName)
>>
>>
>>     if sym != nil {
>>
>>         let f: InitFunction = unsafeBitCast(sym, to: InitFunction.self)
>>
>>         let plugin = f() as? PluginInterface
>>
>>     }
>>
>> }
>>
>> Package.swift file:
>>
>> // swift-tools-version:4.0
>>
>> import PackageDescription
>>
>> let package = Package(
>>
>>     name: "PluginConsumer",
>>
>>     dependencies: [ .package(url: "path_to_plugin_interface", from:
>> "0.0.0") ],
>>
>>     targets: [ .target(name: "PluginConsumer", dependencies: [
>> "PluginConsumer"]) ]
>>
>> )
>>
>>
>> This all compiles nicely, MyPlugin project creates dylib file that
>> executable created by PluginConsumer can load, but the problem is with
>> following line:
>>
>> let plugin = f() as? PluginInterface
>>
>> Type of the plugin is MyPlugin, but from the consumer's view, it doesn't
>> inherit from PluginInterface so I can't call sayHi() method. I assume this
>> is because there is no relation between PluginInterface class that compiler
>> uses for MyPlugin project one that it uses for PluginConsumer project.
>> After library is loaded, they are two completely different classes that
>> happen to share same name. Is my assumption correct and how do I go about
>> fixing it?
>>
>> I had an idea I could make PluginInterface emit dynamic library that
>> would be dynamically linked by both MyPlugin and PluginConsumer, thus
>> making them share same PluginInterface class, but I can't figure out how to
>> do that (or if it's right way of doing this).
>>
>>
>> Any help appreciated :)
>>
>> Lope
>> _______________________________________________
>> swift-users mailing list
>> swift-users at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
>>
>>
>>
> _______________________________________________
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> https://lists.swift.org/mailman/listinfo/swift-users
>
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