[llvm] r211069 - Kill the LLVM global lock.

[Zachary Turner]

This change was reverted in r211072 due to accidentally pushing a whole
branch instead of a single CL.


On Mon, Jun 16, 2014 at 3:40 PM, Zachary Turner <zturner at google.com> wrote:

> Author: zturner
> Date: Mon Jun 16 17:40:42 2014
> New Revision: 211069
>
> URL: http://llvm.org/viewvc/llvm-project?rev=211069&view=rev
> Log:
> Kill the LLVM global lock.
>
> Modified:
>     llvm/trunk/include/llvm/Support/Threading.h
>     llvm/trunk/lib/Support/ManagedStatic.cpp
>     llvm/trunk/lib/Support/Threading.cpp
>     llvm/trunk/lib/Support/Timer.cpp
>
> Modified: llvm/trunk/include/llvm/Support/Threading.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Threading.h?rev=211069&r1=211068&r2=211069&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/Threading.h (original)
> +++ llvm/trunk/include/llvm/Support/Threading.h Mon Jun 16 17:40:42 2014
> @@ -18,9 +18,6 @@
>  #include "llvm/Support/Mutex.h"
>
>  namespace llvm {
> -  /// llvm_get_global_lock - returns the llvm global lock object.
> -  sys::Mutex &llvm_get_global_lock();
> -
>    /// llvm_is_multithreaded - returns true if LLVM is compiled with
> support
>    /// for multiple threads, and false otherwise.
>    bool llvm_is_multithreaded();
>
> Modified: llvm/trunk/lib/Support/ManagedStatic.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/ManagedStatic.cpp?rev=211069&r1=211068&r2=211069&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/ManagedStatic.cpp (original)
> +++ llvm/trunk/lib/Support/ManagedStatic.cpp Mon Jun 16 17:40:42 2014
> @@ -16,16 +16,34 @@
>  #include "llvm/Support/Atomic.h"
>  #include "llvm/Support/MutexGuard.h"
>  #include <cassert>
> +#include <mutex>
>  using namespace llvm;
>
>  static const ManagedStaticBase *StaticList = nullptr;
>
> +// ManagedStatics can get created during execution of static
> constructors.  As a
> +// result, we cannot use a global static std::mutex object for the lock
> since it
> +// may not have been constructed.  Instead, we do a call-once
> initialization of
> +// a pointer to a mutex.  This also means that we must not "initialize"
> the
> +// mutex with nullptr, otherwise it might get reset to nullptr after being
> +// initialized by std::call_once.
> +static std::once_flag MutexInitializationFlag;
> +static std::recursive_mutex *ManagedStaticMutex;
> +
> +namespace {
> +  void InitializeManagedStaticMutex() {
> +    std::call_once(MutexInitializationFlag,
> +        []() { ManagedStaticMutex = new std::recursive_mutex(); });
> +  }
> +}
> +
>  void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
>                                                void (*Deleter)(void*))
> const {
>    assert(Creator);
>    if (llvm_is_multithreaded()) {
> -    llvm::MutexGuard Lock(llvm::llvm_get_global_lock());
> +    InitializeManagedStaticMutex();
>
> +    std::lock_guard<std::recursive_mutex> Lock(*ManagedStaticMutex);
>      if (!Ptr) {
>        void* tmp = Creator();
>
> @@ -74,6 +92,9 @@ void ManagedStaticBase::destroy() const
>
>  /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
>  void llvm::llvm_shutdown() {
> +  InitializeManagedStaticMutex();
> +  std::lock_guard<std::recursive_mutex> Lock(*ManagedStaticMutex);
> +
>    while (StaticList)
>      StaticList->destroy();
>  }
>
> Modified: llvm/trunk/lib/Support/Threading.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Threading.cpp?rev=211069&r1=211068&r2=211069&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/Threading.cpp (original)
> +++ llvm/trunk/lib/Support/Threading.cpp Mon Jun 16 17:40:42 2014
> @@ -20,11 +20,6 @@
>
>  using namespace llvm;
>
> -sys::Mutex& llvm::llvm_get_global_lock() {
> -  static sys::Mutex global_lock;
> -  return global_lock;
> -}
> -
>  bool llvm::llvm_is_multithreaded() {
>  #if LLVM_ENABLE_THREADS != 0
>    return true;
>
> Modified: llvm/trunk/lib/Support/Timer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Timer.cpp?rev=211069&r1=211068&r2=211069&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/Timer.cpp (original)
> +++ llvm/trunk/lib/Support/Timer.cpp Mon Jun 16 17:40:42 2014
> @@ -84,7 +84,7 @@ static TimerGroup *getDefaultTimerGroup(
>    sys::MemoryFence();
>    if (tmp) return tmp;
>
> -  llvm::MutexGuard Lock(llvm::llvm_get_global_lock());
> +  sys::SmartScopedLock<true> Lock(*TimerLock);
>    tmp = DefaultTimerGroup;
>    if (!tmp) {
>      tmp = new TimerGroup("Miscellaneous Ungrouped Timers");
>
>
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