[llvm] r219638 - Removing the static destructor from ManagedStatic.cpp by controlling the allocation and de-allocation of the mutex.

[Iain Sandoe]

Hi Chris,

On 13 Oct 2014, at 23:37, Chris Bieneman wrote:

> Author: cbieneman
> Date: Mon Oct 13 17:37:25 2014
> New Revision: 219638
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=219638&view=rev
> Log:
> Removing the static destructor from ManagedStatic.cpp by controlling the allocation and de-allocation of the mutex.
> 
> This patch adds a new llvm_call_once function which is used by the ManagedStatic implementation to safely initialize a global to avoid static construction and destruction.
> 
> Modified:
>    llvm/trunk/include/llvm/Support/Threading.h
>    llvm/trunk/lib/Support/ManagedStatic.cpp
> 
> Modified: llvm/trunk/include/llvm/Support/Threading.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/Threading.h?rev=219638&r1=219637&r2=219638&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/Threading.h (original)
> +++ llvm/trunk/include/llvm/Support/Threading.h Mon Oct 13 17:37:25 2014
> @@ -15,6 +15,10 @@
> #ifndef LLVM_SUPPORT_THREADING_H
> #define LLVM_SUPPORT_THREADING_H
> 
> +#if !defined(__MINGW__)

did you mean __MINGW__ here ^  or __MINGW32__ ?

> +#include <mutex>
> +#endif
> +
> namespace llvm {
>   /// Returns true if LLVM is compiled with support for multi-threading, and
>   /// false otherwise.
> @@ -33,6 +37,20 @@ namespace llvm {
>   /// the thread stack.
>   void llvm_execute_on_thread(void (*UserFn)(void*), void *UserData,
>                               unsigned RequestedStackSize = 0);
> +
> +template <void (*UserFn)(void)> void llvm_call_once() {
> +
> +#if !defined(__MINGW__)
.. likewise here ^
> +  static std::once_flag flag;
> +  std::call_once(flag, UserFn);
> +
> +#else
> +  struct InitOnceWrapper {
> +    InitOnceWrapper() { UserFn(); }
> +  };
> +  static InitOnceWrapper InitOnceVar;
> +#endif
> +}
> }
> 
> #endif
> 
> Modified: llvm/trunk/lib/Support/ManagedStatic.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/ManagedStatic.cpp?rev=219638&r1=219637&r2=219638&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/ManagedStatic.cpp (original)
> +++ llvm/trunk/lib/Support/ManagedStatic.cpp Mon Oct 13 17:37:25 2014
> @@ -16,16 +16,22 @@
> #include "llvm/Support/Atomic.h"
> #include "llvm/Support/Mutex.h"
> #include "llvm/Support/MutexGuard.h"
> +#include "llvm/Support/Threading.h"
> #include <cassert>
> using namespace llvm;
> 
> static const ManagedStaticBase *StaticList = nullptr;
> +static sys::Mutex *ManagedStaticMutex = nullptr;
> 
> -static sys::Mutex& getManagedStaticMutex() {
> +static void initializeMutex() {
> +  ManagedStaticMutex = new sys::Mutex();
> +}
> +
> +static sys::Mutex* getManagedStaticMutex() {
>   // We need to use a function local static here, since this can get called
>   // during a static constructor and we need to guarantee that it's initialized
>   // correctly.
> -  static sys::Mutex ManagedStaticMutex;
> +  llvm_call_once<initializeMutex>();
>   return ManagedStaticMutex;
> }
> 
> @@ -33,7 +39,7 @@ void ManagedStaticBase::RegisterManagedS
>                                               void (*Deleter)(void*)) const {
>   assert(Creator);
>   if (llvm_is_multithreaded()) {
> -    MutexGuard Lock(getManagedStaticMutex());
> +    MutexGuard Lock(*getManagedStaticMutex());
> 
>     if (!Ptr) {
>       void* tmp = Creator();
> @@ -83,8 +89,13 @@ void ManagedStaticBase::destroy() const
> 
> /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
> void llvm::llvm_shutdown() {
> -  MutexGuard Lock(getManagedStaticMutex());
> +  {
> +    MutexGuard Lock(*getManagedStaticMutex());
> +
> +    while (StaticList)
> +      StaticList->destroy();
> +  }
> 
> -  while (StaticList)
> -    StaticList->destroy();
> +  delete ManagedStaticMutex;
> +  ManagedStaticMutex = nullptr;
> }
> 
> 
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