[llvm] r211287 - Remove support for LLVM runtime multi-threading.
Yaron Keren
yaron.keren at gmail.com
Fri Jun 20 09:46:08 PDT 2014
Running ARCMT clang tests with these two tools stopped working for me after
updating to trunk today, on WIndows 64 bit Visual C++ 2013 building 32 bit
target. They just hang and never finish. I thought initially that's related
to them running in thread but the same happens even if the thread is
disabled in main() and cindextest_main() is called directly.
llvm tests complete OK as are other clang tests that do not use c-arcmt-test
and and c-index-test.
It this possibly related to mutex changes?
Maybe LLVM must be built with threads to support the ARCMT tests?
Yaron
2014-06-20 19:40 GMT+03:00 Zachary Turner <zturner at google.com>:
> It should continue to work. The only thing llvm_start_multithreaded() and
> llvm_stop_multithreaded() did before, despite their names, was to allocate
> a mutex on the heap that served as a global lock. In other words, it
> didn't really do much of anything useful. You could still create threads
> even if you compiled with LLVM_ENABLE_THREADS=0. Some stuff might not have
> been safe for concurrent access, but a) that's not an issue with these
> tests anyway, since they create the thread and then join, so there is no
> concurrency, and b) the areas that were conditionally protected by this
> global lock before are now always protected.
>
> In fact, this makes me wonder if we even need the compile time flag.
>
On Fri, Jun 20, 2014 at 9:34 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
> 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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>> llvm-commits at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>
>
>
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