ThreadLocalModel
public enum ThreadLocalModel
Enumerates the supported models of reference of thread-local variables.
These models are listed from the most general, but least optimized, to the fastest, but most restrictive.
Documentation of these models quotes the Oracle Linker and Libraries Guide.
-
The variable is not thread local and hence has no associated model.
Declaration
Swift
case notThreadLocal
-
Allows reference of all thread-local variables, from either a shared object or a dynamic executable. This model also supports the deferred allocation of a block of thread-local storage when the block is first referenced from a specific thread.
Declaration
Swift
case generalDynamic
-
This model is an optimization of the General Dynamic model. The compiler might determine that a variable is bound locally, or protected, within the object being built. In this case, the compiler instructs the link-editor to statically bind the dynamic
tlsoffsetand use this model.This model provides a performance benefit over the General Dynamic model. Only one call to
tls_get_addr()is required per function, to determine the address ofdtv0,m. The dynamic thread-local storage offset, bound at link-edit time, is added to thedtv0,maddress for each reference.Declaration
Swift
case localDynamic
-
This model can only reference thread-local variables which are available as part of the initial static thread-local template. This template is composed of all thread-local storage blocks that are available at process startup, plus a small backup reservation.
In this model, the thread pointer-relative offset for a given variable
xis stored in the GOT entry for x.This model can reference a limited number of thread-local variables from shared libraries loaded after initial process startup, such as by means of lazy loading, filters, or
dlopen(). This access is satisfied from a fixed backup reservation. This reservation can only provide storage for uninitialized thread-local data items. For maximum flexibility, shared objects should reference thread-local variables using a dynamic model of thread-local storage.Declaration
Swift
case initialExec
-
This model can only reference thread-local variables which are part of the thread-local storage block of the dynamic executable. The link-editor calculates the thread pointer-relative offsets statically, without the need for dynamic relocations, or the extra reference to the GOT. This model can not be used to reference variables outside of the dynamic executable.
Declaration
Swift
case localExec
-
Retrieves the corresponding
LLVMThreadLocalMode.Declaration
Swift
public var llvm: LLVMThreadLocalMode
ThreadLocalModel Enum Reference