lib/Support/CrashRecoveryContext.cpp - third_party/swift-llvm - Git at Google

 //===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/ThreadLocal.h"
 #include <setjmp.h>
 using namespace llvm;

 namespace {

 struct CrashRecoveryContextImpl;

 static ManagedStatic<
     sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext;

 struct CrashRecoveryContextImpl {
   // When threads are disabled, this links up all active
   // CrashRecoveryContextImpls.  When threads are enabled there's one thread
   // per CrashRecoveryContext and CurrentContext is a thread-local, so only one
   // CrashRecoveryContextImpl is active per thread and this is always null.
   const CrashRecoveryContextImpl *Next;

   CrashRecoveryContext *CRC;
   ::jmp_buf JumpBuffer;
   volatile unsigned Failed : 1;
   unsigned SwitchedThread : 1;

 public:
   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
                                                         Failed(false),
                                                         SwitchedThread(false) {
     Next = CurrentContext->get();
     CurrentContext->set(this);
   }
   ~CrashRecoveryContextImpl() {
     if (!SwitchedThread)
       CurrentContext->set(Next);
   }

   /// \brief Called when the separate crash-recovery thread was finished, to
   /// indicate that we don't need to clear the thread-local CurrentContext.
   void setSwitchedThread() {
 #if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
     SwitchedThread = true;
 #endif
   }

   void HandleCrash() {
     // Eliminate the current context entry, to avoid re-entering in case the
     // cleanup code crashes.
     CurrentContext->set(Next);

     assert(!Failed && "Crash recovery context already failed!");
     Failed = true;

     // FIXME: Stash the backtrace.

     // Jump back to the RunSafely we were called under.
     longjmp(JumpBuffer, 1);
   }
 };

 }

 static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex;
 static bool gCrashRecoveryEnabled = false;

 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
        tlIsRecoveringFromCrash;

 static void installExceptionOrSignalHandlers();
 static void uninstallExceptionOrSignalHandlers();

 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}

 CrashRecoveryContext::~CrashRecoveryContext() {
   // Reclaim registered resources.
   CrashRecoveryContextCleanup *i = head;
   const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get();
   tlIsRecoveringFromCrash->set(this);
   while (i) {
     CrashRecoveryContextCleanup *tmp = i;
     i = tmp->next;
     tmp->cleanupFired = true;
     tmp->recoverResources();
     delete tmp;
   }
   tlIsRecoveringFromCrash->set(PC);

   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
   delete CRCI;
 }

 bool CrashRecoveryContext::isRecoveringFromCrash() {
   return tlIsRecoveringFromCrash->get() != nullptr;
 }

 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
   if (!gCrashRecoveryEnabled)
     return nullptr;

   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
   if (!CRCI)
     return nullptr;

   return CRCI->CRC;
 }

 void CrashRecoveryContext::Enable() {
   sys::ScopedLock L(*gCrashRecoveryContextMutex);
   // FIXME: Shouldn't this be a refcount or something?
   if (gCrashRecoveryEnabled)
     return;
   gCrashRecoveryEnabled = true;
   installExceptionOrSignalHandlers();
 }

 void CrashRecoveryContext::Disable() {
   sys::ScopedLock L(*gCrashRecoveryContextMutex);
   if (!gCrashRecoveryEnabled)
     return;
   gCrashRecoveryEnabled = false;
   uninstallExceptionOrSignalHandlers();
 }

 void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
 {
   if (!cleanup)
     return;
   if (head)
     head->prev = cleanup;
   cleanup->next = head;
   head = cleanup;
 }

 void
 CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
   if (!cleanup)
     return;
   if (cleanup == head) {
     head = cleanup->next;
     if (head)
       head->prev = nullptr;
   }
   else {
     cleanup->prev->next = cleanup->next;
     if (cleanup->next)
       cleanup->next->prev = cleanup->prev;
   }
   delete cleanup;
 }

 #if defined(_MSC_VER)
 // If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
 // better than VEH. Vectored exception handling catches all exceptions happening
 // on the thread with installed exception handlers, so it can interfere with
 // internal exception handling of other libraries on that thread. SEH works
 // exactly as you would expect normal exception handling to work: it only
 // catches exceptions if they would bubble out from the stack frame with __try /
 // __except.

 static void installExceptionOrSignalHandlers() {}
 static void uninstallExceptionOrSignalHandlers() {}

 bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
   if (!gCrashRecoveryEnabled) {
     Fn();
     return true;
   }

   bool Result = true;
   __try {
     Fn();
   } __except (1) { // Catch any exception.
     Result = false;
   }
   return Result;
 }

 #else // !_MSC_VER

 #if defined(LLVM_ON_WIN32)
 // This is a non-MSVC compiler, probably mingw gcc or clang without
 // -fms-extensions. Use vectored exception handling (VEH).
 //
 // On Windows, we can make use of vectored exception handling to catch most
 // crashing situations.  Note that this does mean we will be alerted of
 // exceptions *before* structured exception handling has the opportunity to
 // catch it. Unfortunately, this causes problems in practice with other code
 // running on threads with LLVM crash recovery contexts, so we would like to
 // eventually move away from VEH.
 //
 // Vectored works on a per-thread basis, which is an advantage over
 // SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
 // any native support for chaining exception handlers, but VEH allows more than
 // one.
 //
 // The vectored exception handler functionality was added in Windows
 // XP, so if support for older versions of Windows is required,
 // it will have to be added.

 #include "Windows/WindowsSupport.h"

 static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
 {
   // DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
   // compilers and platforms, so we define it manually.
   constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
   switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
   {
   case DBG_PRINTEXCEPTION_C:
   case DbgPrintExceptionWideC:
   case 0x406D1388:  // set debugger thread name
     return EXCEPTION_CONTINUE_EXECUTION;
   }

   // Lookup the current thread local recovery object.
   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

   if (!CRCI) {
     // Something has gone horribly wrong, so let's just tell everyone
     // to keep searching
     CrashRecoveryContext::Disable();
     return EXCEPTION_CONTINUE_SEARCH;
   }

   // TODO: We can capture the stack backtrace here and store it on the
   // implementation if we so choose.

   // Handle the crash
   const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();

   // Note that we don't actually get here because HandleCrash calls
   // longjmp, which means the HandleCrash function never returns.
   llvm_unreachable("Handled the crash, should have longjmp'ed out of here");
 }

 // Because the Enable and Disable calls are static, it means that
 // there may not actually be an Impl available, or even a current
 // CrashRecoveryContext at all.  So we make use of a thread-local
 // exception table.  The handles contained in here will either be
 // non-NULL, valid VEH handles, or NULL.
 static sys::ThreadLocal<const void> sCurrentExceptionHandle;

 static void installExceptionOrSignalHandlers() {
   // We can set up vectored exception handling now.  We will install our
   // handler as the front of the list, though there's no assurances that
   // it will remain at the front (another call could install itself before
   // our handler).  This 1) isn't likely, and 2) shouldn't cause problems.
   PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
   sCurrentExceptionHandle.set(handle);
 }

 static void uninstallExceptionOrSignalHandlers() {
   PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
   if (currentHandle) {
     // Now we can remove the vectored exception handler from the chain
     ::RemoveVectoredExceptionHandler(currentHandle);

     // Reset the handle in our thread-local set.
     sCurrentExceptionHandle.set(NULL);
   }
 }

 #else // !LLVM_ON_WIN32

 // Generic POSIX implementation.
 //
 // This implementation relies on synchronous signals being delivered to the
 // current thread. We use a thread local object to keep track of the active
 // crash recovery context, and install signal handlers to invoke HandleCrash on
 // the active object.
 //
 // This implementation does not to attempt to chain signal handlers in any
 // reliable fashion -- if we get a signal outside of a crash recovery context we
 // simply disable crash recovery and raise the signal again.

 #include <signal.h>

 static const int Signals[] =
     { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
 static const unsigned NumSignals = array_lengthof(Signals);
 static struct sigaction PrevActions[NumSignals];

 static void CrashRecoverySignalHandler(int Signal) {
   // Lookup the current thread local recovery object.
   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

   if (!CRCI) {
     // We didn't find a crash recovery context -- this means either we got a
     // signal on a thread we didn't expect it on, the application got a signal
     // outside of a crash recovery context, or something else went horribly
     // wrong.
     //
     // Disable crash recovery and raise the signal again. The assumption here is
     // that the enclosing application will terminate soon, and we won't want to
     // attempt crash recovery again.
     //
     // This call of Disable isn't thread safe, but it doesn't actually matter.
     CrashRecoveryContext::Disable();
     raise(Signal);

     // The signal will be thrown once the signal mask is restored.
     return;
   }

   // Unblock the signal we received.
   sigset_t SigMask;
   sigemptyset(&SigMask);
   sigaddset(&SigMask, Signal);
   sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);

   if (CRCI)
     const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
 }

 static void installExceptionOrSignalHandlers() {
   // Setup the signal handler.
   struct sigaction Handler;
   Handler.sa_handler = CrashRecoverySignalHandler;
   Handler.sa_flags = 0;
   sigemptyset(&Handler.sa_mask);

   for (unsigned i = 0; i != NumSignals; ++i) {
     sigaction(Signals[i], &Handler, &PrevActions[i]);
   }
 }

 static void uninstallExceptionOrSignalHandlers() {
   // Restore the previous signal handlers.
   for (unsigned i = 0; i != NumSignals; ++i)
     sigaction(Signals[i], &PrevActions[i], nullptr);
 }

 #endif // !LLVM_ON_WIN32

 bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
   // If crash recovery is disabled, do nothing.
   if (gCrashRecoveryEnabled) {
     assert(!Impl && "Crash recovery context already initialized!");
     CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
     Impl = CRCI;

     if (setjmp(CRCI->JumpBuffer) != 0) {
       return false;
     }
   }

   Fn();
   return true;
 }

 #endif // !_MSC_VER

 void CrashRecoveryContext::HandleCrash() {
   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
   assert(CRCI && "Crash recovery context never initialized!");
   CRCI->HandleCrash();
 }

 // FIXME: Portability.
 static void setThreadBackgroundPriority() {
 #ifdef __APPLE__
   setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
 #endif
 }

 static bool hasThreadBackgroundPriority() {
 #ifdef __APPLE__
   return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
 #else
   return false;
 #endif
 }

 namespace {
 struct RunSafelyOnThreadInfo {
   function_ref<void()> Fn;
   CrashRecoveryContext *CRC;
   bool UseBackgroundPriority;
   bool Result;
 };
 }

 static void RunSafelyOnThread_Dispatch(void *UserData) {
   RunSafelyOnThreadInfo *Info =
     reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);

   if (Info->UseBackgroundPriority)
     setThreadBackgroundPriority();

   Info->Result = Info->CRC->RunSafely(Info->Fn);
 }
 bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
                                              unsigned RequestedStackSize) {
   bool UseBackgroundPriority = hasThreadBackgroundPriority();
   RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false };
   llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
   if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl)
     CRC->setSwitchedThread();
   return Info.Result;
 }
	//===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Support/CrashRecoveryContext.h"
	#include "llvm/Config/config.h"
	#include "llvm/Support/ErrorHandling.h"
	#include "llvm/Support/ManagedStatic.h"
	#include "llvm/Support/Mutex.h"
	#include "llvm/Support/ThreadLocal.h"
	#include <setjmp.h>
	using namespace llvm;

	namespace {

	struct CrashRecoveryContextImpl;

	static ManagedStatic<
	sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext;

	struct CrashRecoveryContextImpl {
	// When threads are disabled, this links up all active
	// CrashRecoveryContextImpls. When threads are enabled there's one thread
	// per CrashRecoveryContext and CurrentContext is a thread-local, so only one
	// CrashRecoveryContextImpl is active per thread and this is always null.
	const CrashRecoveryContextImpl *Next;

	CrashRecoveryContext *CRC;
	::jmp_buf JumpBuffer;
	volatile unsigned Failed : 1;
	unsigned SwitchedThread : 1;

	public:
	CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
	Failed(false),
	SwitchedThread(false) {
	Next = CurrentContext->get();
	CurrentContext->set(this);
	}
	~CrashRecoveryContextImpl() {
	if (!SwitchedThread)
	CurrentContext->set(Next);
	}

	/// \brief Called when the separate crash-recovery thread was finished, to
	/// indicate that we don't need to clear the thread-local CurrentContext.
	void setSwitchedThread() {
	#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
	SwitchedThread = true;
	#endif
	}

	void HandleCrash() {
	// Eliminate the current context entry, to avoid re-entering in case the
	// cleanup code crashes.
	CurrentContext->set(Next);

	assert(!Failed && "Crash recovery context already failed!");
	Failed = true;

	// FIXME: Stash the backtrace.

	// Jump back to the RunSafely we were called under.
	longjmp(JumpBuffer, 1);
	}
	};

	}

	static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex;
	static bool gCrashRecoveryEnabled = false;

	static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
	tlIsRecoveringFromCrash;

	static void installExceptionOrSignalHandlers();
	static void uninstallExceptionOrSignalHandlers();

	CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}

	CrashRecoveryContext::~CrashRecoveryContext() {
	// Reclaim registered resources.
	CrashRecoveryContextCleanup *i = head;
	const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get();
	tlIsRecoveringFromCrash->set(this);
	while (i) {
	CrashRecoveryContextCleanup *tmp = i;
	i = tmp->next;
	tmp->cleanupFired = true;
	tmp->recoverResources();
	delete tmp;
	}
	tlIsRecoveringFromCrash->set(PC);

	CrashRecoveryContextImpl CRCI = (CrashRecoveryContextImpl ) Impl;
	delete CRCI;
	}

	bool CrashRecoveryContext::isRecoveringFromCrash() {
	return tlIsRecoveringFromCrash->get() != nullptr;
	}

	CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
	if (!gCrashRecoveryEnabled)
	return nullptr;

	const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
	if (!CRCI)
	return nullptr;

	return CRCI->CRC;
	}

	void CrashRecoveryContext::Enable() {
	sys::ScopedLock L(*gCrashRecoveryContextMutex);
	// FIXME: Shouldn't this be a refcount or something?
	if (gCrashRecoveryEnabled)
	return;
	gCrashRecoveryEnabled = true;
	installExceptionOrSignalHandlers();
	}

	void CrashRecoveryContext::Disable() {
	sys::ScopedLock L(*gCrashRecoveryContextMutex);
	if (!gCrashRecoveryEnabled)
	return;
	gCrashRecoveryEnabled = false;
	uninstallExceptionOrSignalHandlers();
	}

	void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
	{
	if (!cleanup)
	return;
	if (head)
	head->prev = cleanup;
	cleanup->next = head;
	head = cleanup;
	}

	void
	CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
	if (!cleanup)
	return;
	if (cleanup == head) {
	head = cleanup->next;
	if (head)
	head->prev = nullptr;
	}
	else {
	cleanup->prev->next = cleanup->next;
	if (cleanup->next)
	cleanup->next->prev = cleanup->prev;
	}
	delete cleanup;
	}

	#if defined(_MSC_VER)
	// If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
	// better than VEH. Vectored exception handling catches all exceptions happening
	// on the thread with installed exception handlers, so it can interfere with
	// internal exception handling of other libraries on that thread. SEH works
	// exactly as you would expect normal exception handling to work: it only
	// catches exceptions if they would bubble out from the stack frame with __try /
	// __except.

	static void installExceptionOrSignalHandlers() {}
	static void uninstallExceptionOrSignalHandlers() {}

	bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
	if (!gCrashRecoveryEnabled) {
	Fn();
	return true;
	}

	bool Result = true;
	__try {
	Fn();
	} __except (1) { // Catch any exception.
	Result = false;
	}
	return Result;
	}

	#else // !_MSC_VER

	#if defined(LLVM_ON_WIN32)
	// This is a non-MSVC compiler, probably mingw gcc or clang without
	// -fms-extensions. Use vectored exception handling (VEH).
	//
	// On Windows, we can make use of vectored exception handling to catch most
	// crashing situations. Note that this does mean we will be alerted of
	// exceptions before structured exception handling has the opportunity to
	// catch it. Unfortunately, this causes problems in practice with other code
	// running on threads with LLVM crash recovery contexts, so we would like to
	// eventually move away from VEH.
	//
	// Vectored works on a per-thread basis, which is an advantage over
	// SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
	// any native support for chaining exception handlers, but VEH allows more than
	// one.
	//
	// The vectored exception handler functionality was added in Windows
	// XP, so if support for older versions of Windows is required,
	// it will have to be added.

	#include "Windows/WindowsSupport.h"

	static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
	{
	// DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
	// compilers and platforms, so we define it manually.
	constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
	switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
	{
	case DBG_PRINTEXCEPTION_C:
	case DbgPrintExceptionWideC:
	case 0x406D1388: // set debugger thread name
	return EXCEPTION_CONTINUE_EXECUTION;
	}

	// Lookup the current thread local recovery object.
	const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

	if (!CRCI) {
	// Something has gone horribly wrong, so let's just tell everyone
	// to keep searching
	CrashRecoveryContext::Disable();
	return EXCEPTION_CONTINUE_SEARCH;
	}

	// TODO: We can capture the stack backtrace here and store it on the
	// implementation if we so choose.

	// Handle the crash
	const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();

	// Note that we don't actually get here because HandleCrash calls
	// longjmp, which means the HandleCrash function never returns.
	llvm_unreachable("Handled the crash, should have longjmp'ed out of here");
	}

	// Because the Enable and Disable calls are static, it means that
	// there may not actually be an Impl available, or even a current
	// CrashRecoveryContext at all. So we make use of a thread-local
	// exception table. The handles contained in here will either be
	// non-NULL, valid VEH handles, or NULL.
	static sys::ThreadLocal<const void> sCurrentExceptionHandle;

	static void installExceptionOrSignalHandlers() {
	// We can set up vectored exception handling now. We will install our
	// handler as the front of the list, though there's no assurances that
	// it will remain at the front (another call could install itself before
	// our handler). This 1) isn't likely, and 2) shouldn't cause problems.
	PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
	sCurrentExceptionHandle.set(handle);
	}

	static void uninstallExceptionOrSignalHandlers() {
	PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
	if (currentHandle) {
	// Now we can remove the vectored exception handler from the chain
	::RemoveVectoredExceptionHandler(currentHandle);

	// Reset the handle in our thread-local set.
	sCurrentExceptionHandle.set(NULL);
	}
	}

	#else // !LLVM_ON_WIN32

	// Generic POSIX implementation.
	//
	// This implementation relies on synchronous signals being delivered to the
	// current thread. We use a thread local object to keep track of the active
	// crash recovery context, and install signal handlers to invoke HandleCrash on
	// the active object.
	//
	// This implementation does not to attempt to chain signal handlers in any
	// reliable fashion -- if we get a signal outside of a crash recovery context we
	// simply disable crash recovery and raise the signal again.

	#include <signal.h>

	static const int Signals[] =
	{ SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
	static const unsigned NumSignals = array_lengthof(Signals);
	static struct sigaction PrevActions[NumSignals];

	static void CrashRecoverySignalHandler(int Signal) {
	// Lookup the current thread local recovery object.
	const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

	if (!CRCI) {
	// We didn't find a crash recovery context -- this means either we got a
	// signal on a thread we didn't expect it on, the application got a signal
	// outside of a crash recovery context, or something else went horribly
	// wrong.
	//
	// Disable crash recovery and raise the signal again. The assumption here is
	// that the enclosing application will terminate soon, and we won't want to
	// attempt crash recovery again.
	//
	// This call of Disable isn't thread safe, but it doesn't actually matter.
	CrashRecoveryContext::Disable();
	raise(Signal);

	// The signal will be thrown once the signal mask is restored.
	return;
	}

	// Unblock the signal we received.
	sigset_t SigMask;
	sigemptyset(&SigMask);
	sigaddset(&SigMask, Signal);
	sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);

	if (CRCI)
	const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
	}

	static void installExceptionOrSignalHandlers() {
	// Setup the signal handler.
	struct sigaction Handler;
	Handler.sa_handler = CrashRecoverySignalHandler;
	Handler.sa_flags = 0;
	sigemptyset(&Handler.sa_mask);

	for (unsigned i = 0; i != NumSignals; ++i) {
	sigaction(Signals[i], &Handler, &PrevActions[i]);
	}
	}

	static void uninstallExceptionOrSignalHandlers() {
	// Restore the previous signal handlers.
	for (unsigned i = 0; i != NumSignals; ++i)
	sigaction(Signals[i], &PrevActions[i], nullptr);
	}

	#endif // !LLVM_ON_WIN32

	bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
	// If crash recovery is disabled, do nothing.
	if (gCrashRecoveryEnabled) {
	assert(!Impl && "Crash recovery context already initialized!");
	CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
	Impl = CRCI;

	if (setjmp(CRCI->JumpBuffer) != 0) {
	return false;
	}
	}

	Fn();
	return true;
	}

	#endif // !_MSC_VER

	void CrashRecoveryContext::HandleCrash() {
	CrashRecoveryContextImpl CRCI = (CrashRecoveryContextImpl ) Impl;
	assert(CRCI && "Crash recovery context never initialized!");
	CRCI->HandleCrash();
	}

	// FIXME: Portability.
	static void setThreadBackgroundPriority() {
	#ifdef __APPLE__
	setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
	#endif
	}

	static bool hasThreadBackgroundPriority() {
	#ifdef __APPLE__
	return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
	#else
	return false;
	#endif
	}

	namespace {
	struct RunSafelyOnThreadInfo {
	function_ref<void()> Fn;
	CrashRecoveryContext *CRC;
	bool UseBackgroundPriority;
	bool Result;
	};
	}

	static void RunSafelyOnThread_Dispatch(void *UserData) {
	RunSafelyOnThreadInfo *Info =
	reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);

	if (Info->UseBackgroundPriority)
	setThreadBackgroundPriority();

	Info->Result = Info->CRC->RunSafely(Info->Fn);
	}
	bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
	unsigned RequestedStackSize) {
	bool UseBackgroundPriority = hasThreadBackgroundPriority();
	RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false };
	llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
	if (CrashRecoveryContextImpl CRC = (CrashRecoveryContextImpl )Impl)
	CRC->setSwitchedThread();
	return Info.Result;
	}