From a4d0ff9cd1fb3fe4c3a58d0747dc523f7d9e9e3f Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Thu, 19 Jun 2014 18:18:23 +0000 Subject: Remove support for LLVM runtime multi-threading. After a number of previous small iterations, the functions llvm_start_multithreaded() and llvm_stop_multithreaded() have been reduced essentially to no-ops. This change removes them entirely. Reviewed by: rnk, dblaikie Differential Revision: http://reviews.llvm.org/D4216 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211287 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/ProgrammersManual.rst | 45 ++++----------------------------------------- 1 file changed, 4 insertions(+), 41 deletions(-) (limited to 'docs') diff --git a/docs/ProgrammersManual.rst b/docs/ProgrammersManual.rst index df3795a34d..a7b28b36ca 100644 --- a/docs/ProgrammersManual.rst +++ b/docs/ProgrammersManual.rst @@ -2170,46 +2170,13 @@ compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and using the resultant compiler to build a copy of LLVM with multithreading support. -.. _startmultithreaded: - -Entering and Exiting Multithreaded Mode ---------------------------------------- - -In order to properly protect its internal data structures while avoiding -excessive locking overhead in the single-threaded case, the LLVM must intialize -certain data structures necessary to provide guards around its internals. To do -so, the client program must invoke ``llvm_start_multithreaded()`` before making -any concurrent LLVM API calls. To subsequently tear down these structures, use -the ``llvm_stop_multithreaded()`` call. You can also use the -``llvm_is_multithreaded()`` call to check the status of multithreaded mode. - -Note that both of these calls must be made *in isolation*. That is to say that -no other LLVM API calls may be executing at any time during the execution of -``llvm_start_multithreaded()`` or ``llvm_stop_multithreaded``. It is the -client's responsibility to enforce this isolation. - -The return value of ``llvm_start_multithreaded()`` indicates the success or -failure of the initialization. Failure typically indicates that your copy of -LLVM was built without multithreading support, typically because GCC atomic -intrinsics were not found in your system compiler. In this case, the LLVM API -will not be safe for concurrent calls. However, it *will* be safe for hosting -threaded applications in the JIT, though :ref:`care must be taken -` to ensure that side exits and the like do not accidentally -result in concurrent LLVM API calls. - .. _shutdown: Ending Execution with ``llvm_shutdown()`` ----------------------------------------- When you are done using the LLVM APIs, you should call ``llvm_shutdown()`` to -deallocate memory used for internal structures. This will also invoke -``llvm_stop_multithreaded()`` if LLVM is operating in multithreaded mode. As -such, ``llvm_shutdown()`` requires the same isolation guarantees as -``llvm_stop_multithreaded()``. - -Note that, if you use scope-based shutdown, you can use the -``llvm_shutdown_obj`` class, which calls ``llvm_shutdown()`` in its destructor. +deallocate memory used for internal structures. .. _managedstatic: @@ -2217,15 +2184,11 @@ Lazy Initialization with ``ManagedStatic`` ------------------------------------------ ``ManagedStatic`` is a utility class in LLVM used to implement static -initialization of static resources, such as the global type tables. Before the -invocation of ``llvm_shutdown()``, it implements a simple lazy initialization -scheme. Once ``llvm_start_multithreaded()`` returns, however, it uses +initialization of static resources, such as the global type tables. In a +single-threaded environment, it implements a simple lazy initialization scheme. +When LLVM is compiled with support for multi-threading, however, it uses double-checked locking to implement thread-safe lazy initialization. -Note that, because no other threads are allowed to issue LLVM API calls before -``llvm_start_multithreaded()`` returns, it is possible to have -``ManagedStatic``\ s of ``llvm::sys::Mutex``\ s. - .. _llvmcontext: Achieving Isolation with ``LLVMContext`` -- cgit v1.2.3