[llvm] r211287 - Remove support for LLVM runtime multi-threading.
Yaron Keren
yaron.keren at gmail.com
Fri Jun 20 09:34:38 PDT 2014
Hi,
Two of the clang test tools, c-arcmt-test and and c-index-test always run
the test through one thread only:
/* We intentionally run in a separate thread to ensure we at least minimal
* testing of a multithreaded environment (for example, having a reduced
stack
* size). */
If LLVM/clang were built without thread support, can these tools continue
the same?
Yaron
2014-06-19 21:18 GMT+03:00 Zachary Turner <zturner at google.com>:
> Author: zturner
> Date: Thu Jun 19 13:18:23 2014
> New Revision: 211287
>
> URL: http://llvm.org/viewvc/llvm-project?rev=211287&view=rev
> Log:
> 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
>
> Modified:
> llvm/trunk/docs/ProgrammersManual.rst
> llvm/trunk/include/llvm-c/Core.h
> llvm/trunk/include/llvm/Support/ManagedStatic.h
> llvm/trunk/include/llvm/Support/Threading.h
> llvm/trunk/lib/IR/Core.cpp
> llvm/trunk/lib/Support/Threading.cpp
> llvm/trunk/unittests/Support/ManagedStatic.cpp
>
> Modified: llvm/trunk/docs/ProgrammersManual.rst
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/ProgrammersManual.rst?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/docs/ProgrammersManual.rst (original)
> +++ llvm/trunk/docs/ProgrammersManual.rst Thu Jun 19 13:18:23 2014
> @@ -2170,46 +2170,13 @@ compiler, consider compiling LLVM and LL
> 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``
>
> Modified: llvm/trunk/include/llvm-c/Core.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm-c/Core.h?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm-c/Core.h (original)
> +++ llvm/trunk/include/llvm-c/Core.h Thu Jun 19 13:18:23 2014
> @@ -2848,16 +2848,13 @@ void LLVMDisposePassManager(LLVMPassMana
> * @{
> */
>
> -/** Allocate and initialize structures needed to make LLVM safe for
> - multithreading. The return value indicates whether multithreaded
> - initialization succeeded. Must be executed in isolation from all
> - other LLVM api calls.
> - @see llvm::llvm_start_multithreaded */
> +/** Deprecated: Multi-threading can only be enabled/disabled with the
> compile
> + time define LLVM_ENABLE_THREADS. This function always returns
> + LLVMIsMultithreaded(). */
> LLVMBool LLVMStartMultithreaded(void);
>
> -/** Deallocate structures necessary to make LLVM safe for multithreading.
> - Must be executed in isolation from all other LLVM api calls.
> - @see llvm::llvm_stop_multithreaded */
> +/** Deprecated: Multi-threading can only be enabled/disabled with the
> compile
> + time define LLVM_ENABLE_THREADS. */
> void LLVMStopMultithreaded(void);
>
> /** Check whether LLVM is executing in thread-safe mode or not.
>
> Modified: llvm/trunk/include/llvm/Support/ManagedStatic.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/ManagedStatic.h?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/ManagedStatic.h (original)
> +++ llvm/trunk/include/llvm/Support/ManagedStatic.h Thu Jun 19 13:18:23
> 2014
> @@ -103,9 +103,6 @@ void llvm_shutdown();
> /// llvm_shutdown() when it is destroyed.
> struct llvm_shutdown_obj {
> llvm_shutdown_obj() { }
> - explicit llvm_shutdown_obj(bool multithreaded) {
> - if (multithreaded) llvm_start_multithreaded();
> - }
> ~llvm_shutdown_obj() { llvm_shutdown(); }
> };
>
>
> Modified: llvm/trunk/include/llvm/Support/Threading.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Threading.h?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/Threading.h (original)
> +++ llvm/trunk/include/llvm/Support/Threading.h Thu Jun 19 13:18:23 2014
> @@ -7,30 +7,19 @@
> //
>
> //===----------------------------------------------------------------------===//
> //
> -// TThis file defines llvm_start_multithreaded() and friends.
> +// This file declares helper functions for running LLVM in a
> multi-threaded
> +// environment.
> //
>
> //===----------------------------------------------------------------------===//
>
> #ifndef LLVM_SUPPORT_THREADING_H
> #define LLVM_SUPPORT_THREADING_H
>
> -namespace llvm {
> - /// llvm_start_multithreaded - Allocate and initialize structures
> needed to
> - /// make LLVM safe for multithreading. The return value indicates
> whether
> - /// multithreaded initialization succeeded. LLVM will still be
> operational
> - /// on "failed" return, and will still be safe for hosting threading
> - /// applications in the JIT, but will not be safe for concurrent calls
> to the
> - /// LLVM APIs.
> - /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
> - bool llvm_start_multithreaded();
> -
> - /// llvm_stop_multithreaded - Deallocate structures necessary to make
> LLVM
> - /// safe for multithreading.
> - /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
> - void llvm_stop_multithreaded();
> +#include "llvm/Support/Mutex.h"
>
> - /// llvm_is_multithreaded - Check whether LLVM is executing in
> thread-safe
> - /// mode or not.
> +namespace llvm {
> + /// Returns true if LLVM is compiled with support for multi-threading,
> and
> + /// false otherwise.
> bool llvm_is_multithreaded();
>
> /// llvm_execute_on_thread - Execute the given \p UserFn on a separate
>
> Modified: llvm/trunk/lib/IR/Core.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Core.cpp?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/IR/Core.cpp (original)
> +++ llvm/trunk/lib/IR/Core.cpp Thu Jun 19 13:18:23 2014
> @@ -2702,11 +2702,10 @@ void LLVMDisposePassManager(LLVMPassMana
> /*===-- Threading
> ------------------------------------------------------===*/
>
> LLVMBool LLVMStartMultithreaded() {
> - return llvm_start_multithreaded();
> + return LLVMIsMultithreaded();
> }
>
> void LLVMStopMultithreaded() {
> - llvm_stop_multithreaded();
> }
>
> LLVMBool LLVMIsMultithreaded() {
>
> Modified: llvm/trunk/lib/Support/Threading.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Threading.cpp?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/Threading.cpp (original)
> +++ llvm/trunk/lib/Support/Threading.cpp Thu Jun 19 13:18:23 2014
> @@ -7,7 +7,8 @@
> //
>
> //===----------------------------------------------------------------------===//
> //
> -// This file implements llvm_start_multithreaded() and friends.
> +// This file defines helper functions for running LLVM in a multi-threaded
> +// environment.
> //
>
> //===----------------------------------------------------------------------===//
>
> @@ -19,38 +20,14 @@
>
> using namespace llvm;
>
> -static bool multithreaded_mode = false;
> -
> -bool llvm::llvm_start_multithreaded() {
> +bool llvm::llvm_is_multithreaded() {
> #if LLVM_ENABLE_THREADS != 0
> - assert(!multithreaded_mode && "Already multithreaded!");
> - multithreaded_mode = true;
> -
> - // We fence here to ensure that all initialization is complete BEFORE we
> - // return from llvm_start_multithreaded().
> - sys::MemoryFence();
> return true;
> #else
> return false;
> #endif
> }
>
> -void llvm::llvm_stop_multithreaded() {
> -#if LLVM_ENABLE_THREADS != 0
> - assert(multithreaded_mode && "Not currently multithreaded!");
> -
> - // We fence here to insure that all threaded operations are complete
> BEFORE we
> - // return from llvm_stop_multithreaded().
> - sys::MemoryFence();
> -
> - multithreaded_mode = false;
> -#endif
> -}
> -
> -bool llvm::llvm_is_multithreaded() {
> - return multithreaded_mode;
> -}
> -
> #if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
> #include <pthread.h>
>
>
> Modified: llvm/trunk/unittests/Support/ManagedStatic.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/ManagedStatic.cpp?rev=211287&r1=211286&r2=211287&view=diff
>
> ==============================================================================
> --- llvm/trunk/unittests/Support/ManagedStatic.cpp (original)
> +++ llvm/trunk/unittests/Support/ManagedStatic.cpp Thu Jun 19 13:18:23 2014
> @@ -47,7 +47,6 @@ TEST(Initialize, MultipleThreads) {
> void *p1 = test1::allocate_stack(a1);
> void *p2 = test1::allocate_stack(a2);
>
> - llvm_start_multithreaded();
> pthread_t t1, t2;
> pthread_create(&t1, &a1, test1::helper, nullptr);
> pthread_create(&t2, &a2, test1::helper, nullptr);
> @@ -55,7 +54,6 @@ TEST(Initialize, MultipleThreads) {
> pthread_join(t2, nullptr);
> free(p1);
> free(p2);
> - llvm_stop_multithreaded();
> }
> #endif
>
>
>
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