[PATCH] D30107: Refactor DynamicLibrary so searching for a symbol will have a defined order and libraries are properly unloaded when llvm_shutdown is called.

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


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Comment at: llvm/trunk/include/llvm/Support/DynamicLibrary.h:61
     /// This function permanently loads the dynamic library at the given path.
-    /// The library will only be unloaded when the program terminates.
+    /// The library will only be unloaded when llvm_shutdown() is called.
     /// This returns a valid DynamicLibrary instance on success and an invalid
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marsupial wrote:
> efriedma wrote:
> > Is this change necessary?  I don't see any discussion of this in the review.
> > 
> > In addition to being used by the JIT, this API is used to load plugins, and unloading a plugin during llvm_shutdown() can cause a segfault, depending on the order globals get destroyed.
> I can see the benefit of DynamicLibrary::HandleSet::~HandleSet iterating in reverse order, but having LLVM release memory when I explicitly tell it I'm not using LLVM anymore is important.
> 
> Not releasing / deallocating the libraries seems to be a violation of the documentation:
> "When you are done using the LLVM APIs, you should call llvm_shutdown() to deallocate memory used for internal structures."
> 
> If there are issues with plugins wouldn't it better handled in the plugin interface with a way to signal shutdown will/is occurring.
Adding an interface to notify plugins of an impending shutdown wouldn't help. The problem is that llvm_shutdown itself tries to call into code in the plugin, and there's no way to unregister those handlers.  It might be possible to refactor a bunch of code to allow unloading a plugin without calling llvm_shutdown, but that would be complicated, for little benefit.

Maybe we could delay unloading shared libraries until other code like the pass manager finishes shutdown?


Repository:
  rL LLVM

https://reviews.llvm.org/D30107