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authorZachary Turner <zturner@google.com>2014-06-19 18:18:23 +0000
committerZachary Turner <zturner@google.com>2014-06-19 18:18:23 +0000
commita4d0ff9cd1fb3fe4c3a58d0747dc523f7d9e9e3f (patch)
tree7a5b3038c8c592ee3a6c580e872a31b9378fbd6a /docs
parent6072096fd63c1996cfe731ecddcb6b3232e37b70 (diff)
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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
Diffstat (limited to 'docs')
-rw-r--r--docs/ProgrammersManual.rst45
1 files changed, 4 insertions, 41 deletions
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
-<jitthreading>` 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``