/LazyModulesExample

Primary LanguageSwift

LazyModulesExample

This demo project is here for educational purposes and contains mvp code, that can be vastly improved.

It demonstrates the following features:

  • Lazy modules loading
  • Modules merging

Both of them show you the ways of reducing the dynamic libaries count, which dyld loads during the application start.

Another solution is to turn all modules from dynamic frameworks into static libraries, but this is not that fun =).

Build the project and check the contents of your LazyModulesExample.app/Frameworks folder.

You will see Feature1.framework, Feature2.framework and MergedCore.framework (and probably several libswift.dylibs, depending on versions of your Xcode and target iOS).

During the application start only system libraries and MergedCore.framework will be loaded into memory. Feature1.framework and Feature2.framework will be loaded on demand at runtime (i.e. lazily).

Lazy modules loading

  1. Launch the app and tap "LOAD FEATURE 1" or "LOAD FEATURE 2" button.

  2. Check the console logs. You will see something like

!!!
  Will load Feature1 if it is not loaded yet.
  See dyld logs in the console.
  ...
!!!

dyld: loaded: /Users/username/Library/Developer/Xcode/DerivedData/LazyModulesExample-giiydmraztexwgcipbutixergqns/Build/Products/Debug-iphonesimulator/Feature1.framework/Feature1

In Feature1. Printing from class named: Protocol1Impl

What this means, is that dynamic linker (dyld) loaded a framework from the disk into memory. See LazyModulesLoader.m for some implementation details.

  1. If you did not see what was mentioned above, then make sure 'Dynamic Library Loads' is enabled in 'Scheme -> Run -> Diagnostics', or pass 'DYLD_PRINT_LIBRRARIES' environment variable in 'Scheme -> Run -> Arguments -> Eviromnent Variables'.

Modules hierarchy

  1. Feature1 - lazily loaded module.
  2. Feature2 - lazily loaded module.
  3. Interfaces - a mediator module to allow communication between feature modules (features do not depend on each other, they depend on Interfaces).
  4. DI - dependency injection module. Also implements lazy loading of other modules.
  5. Footprints - module to feed DI with information about which lazy module to load in response on a resolve() request.
  6. MergedCore - module in which we merge DI, Interfaces and Footprints.

Modules merging

Modules merging is based on the technique described in Amimono cocoapods plugin.

We merge DI, Interfaces and Footprints into MergedCore.

  1. See MergedCore.xcconfig with its -filelist flag passed to the static linker (ld).
  2. See Create filelist per architecture build phase of MergedCore target to understand how this filelist gets filled.
  3. See Check for dublicated symbols absence build phase of LazyModulesExample target to understand how we make sure no dublicated symbols get bundled in the application. This may happen if you accidentally break the project via copying DI.framework into the LazyModulesExample.app/Frameworks folder and linking LazyModulesExample.app/LazyModulesExample against DI.framework/DI while still linking against MergedCore.framework/MergedCore.