Revert upstream libcxxrt commit which can cause hangs on i386
This reverts upstream commit fd484be:
Atomics cleanup (#11)
We need to test exception specifiers but they're gone in C++17 so
compile the tests with an older version of the standard.
Rewrite the guard logic to be more idiomatic C++ and more
comprehensible and make sure that atomics are used where necessary.
It looks like there are some corner cases in the i386 and/or 32-bit
atomics handling, which can make __cxa_guard_acquire() hang in certain
situations.
Reported by: antoine
Obtained from: https://github.com/libcxxrt/libcxxrt/commit/fd484be
Fixes: 56aaed388b
MFC after: 2 weeks
This commit is contained in:
parent
e39ec8933b
commit
2548237983
@ -1,102 +1,30 @@
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#ifndef __has_builtin
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#ifndef __has_builtin
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# define __has_builtin(x) 0
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#define __has_builtin(x) 0
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#endif
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#endif
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#ifndef __has_feature
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#ifndef __has_feature
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# define __has_feature(x) 0
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#define __has_feature(x) 0
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#endif
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#ifndef __has_extension
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# define __has_extension(x) 0
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#endif
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#if !__has_extension(c_atomic)
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# define _Atomic(T) T
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#endif
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#endif
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/**
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* Swap macro that enforces a happens-before relationship with a corresponding
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* ATOMIC_LOAD.
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*/
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#if __has_builtin(__c11_atomic_exchange)
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#if __has_builtin(__c11_atomic_exchange)
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# define ATOMIC_BUILTIN(name) __c11_atomic_##name
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#define ATOMIC_SWAP(addr, val)\
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__c11_atomic_exchange(reinterpret_cast<_Atomic(__typeof__(val))*>(addr), val, __ATOMIC_ACQ_REL)
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#elif __has_builtin(__sync_swap)
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#define ATOMIC_SWAP(addr, val)\
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__sync_swap(addr, val)
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#else
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#else
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# define ATOMIC_BUILTIN(name) __atomic_##name##_n
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#define ATOMIC_SWAP(addr, val)\
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__sync_lock_test_and_set(addr, val)
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#endif
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#endif
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namespace
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#if __has_builtin(__c11_atomic_load)
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{
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#define ATOMIC_LOAD(addr)\
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/**
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__c11_atomic_load(reinterpret_cast<_Atomic(__typeof__(*addr))*>(addr), __ATOMIC_ACQUIRE)
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* C++11 memory orders. We only need a subset of them.
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*/
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enum memory_order
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{
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/**
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* Acquire order.
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*/
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acquire = __ATOMIC_ACQUIRE,
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/**
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* Release order.
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*/
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release = __ATOMIC_RELEASE,
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/**
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* Sequentially consistent memory ordering.
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*/
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seqcst = __ATOMIC_SEQ_CST
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};
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/**
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* Atomic, implements a subset of `std::atomic`.
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*/
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template<typename T>
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class atomic
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{
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/**
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* The underlying value. Use C11 atomic qualification if available.
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*/
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_Atomic(T) val;
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public:
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/**
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* Constructor, takes a value.
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*/
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atomic(T init) : val(init) {}
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/**
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* Atomically load with the specified memory order.
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*/
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T load(memory_order order = memory_order::seqcst)
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{
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return ATOMIC_BUILTIN(load)(&val, order);
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}
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/**
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* Atomically store with the specified memory order.
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*/
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void store(T v, memory_order order = memory_order::seqcst)
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{
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return ATOMIC_BUILTIN(store)(&val, v, order);
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}
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/**
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* Atomically exchange with the specified memory order.
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*/
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T exchange(T v, memory_order order = memory_order::seqcst)
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{
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return ATOMIC_BUILTIN(exchange)(&val, v, order);
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}
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/**
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* Atomically exchange with the specified memory order.
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*/
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bool compare_exchange(T & expected,
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T desired,
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memory_order order = memory_order::seqcst)
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{
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#if __has_builtin(__c11_atomic_compare_exchange_strong)
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return __c11_atomic_compare_exchange_strong(
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&val, &expected, desired, order, order);
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#else
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#else
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return __atomic_compare_exchange_n(
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#define ATOMIC_LOAD(addr)\
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&val, &expected, desired, true, order, order);
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(__sync_synchronize(), *addr)
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#endif
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#endif
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}
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};
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} // namespace
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#undef ATOMIC_BUILTIN
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@ -1,6 +1,5 @@
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/*
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/*
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* Copyright 2010-2011 PathScale, Inc. All rights reserved.
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* Copyright 2010-2011 PathScale, Inc. All rights reserved.
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* Copyright 2021 David Chisnall. All rights reserved.
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*
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*
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* Redistribution and use in source and binary forms, with or without
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* modification, are permitted provided that the following conditions are met:
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@ -290,9 +289,9 @@ using namespace ABI_NAMESPACE;
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/** The global termination handler. */
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/** The global termination handler. */
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static atomic<terminate_handler> terminateHandler = abort;
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static terminate_handler terminateHandler = abort;
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/** The global unexpected exception handler. */
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/** The global unexpected exception handler. */
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static atomic<unexpected_handler> unexpectedHandler = std::terminate;
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static unexpected_handler unexpectedHandler = std::terminate;
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/** Key used for thread-local data. */
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/** Key used for thread-local data. */
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static pthread_key_t eh_key;
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static pthread_key_t eh_key;
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@ -745,12 +744,12 @@ static void throw_exception(__cxa_exception *ex)
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ex->unexpectedHandler = info->unexpectedHandler;
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ex->unexpectedHandler = info->unexpectedHandler;
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if (0 == ex->unexpectedHandler)
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if (0 == ex->unexpectedHandler)
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{
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{
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ex->unexpectedHandler = unexpectedHandler.load();
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ex->unexpectedHandler = unexpectedHandler;
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}
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}
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ex->terminateHandler = info->terminateHandler;
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ex->terminateHandler = info->terminateHandler;
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if (0 == ex->terminateHandler)
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if (0 == ex->terminateHandler)
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{
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{
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ex->terminateHandler = terminateHandler.load();
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ex->terminateHandler = terminateHandler;
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}
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}
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info->globals.uncaughtExceptions++;
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info->globals.uncaughtExceptions++;
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@ -1450,7 +1449,7 @@ namespace std
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{
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{
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if (thread_local_handlers) { return pathscale::set_unexpected(f); }
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if (thread_local_handlers) { return pathscale::set_unexpected(f); }
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return unexpectedHandler.exchange(f);
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return ATOMIC_SWAP(&unexpectedHandler, f);
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}
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}
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/**
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/**
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* Sets the function that is called to terminate the program.
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* Sets the function that is called to terminate the program.
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@ -1459,7 +1458,7 @@ namespace std
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{
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{
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if (thread_local_handlers) { return pathscale::set_terminate(f); }
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if (thread_local_handlers) { return pathscale::set_terminate(f); }
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return terminateHandler.exchange(f);
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return ATOMIC_SWAP(&terminateHandler, f);
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}
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}
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/**
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/**
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* Terminates the program, calling a custom terminate implementation if
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* Terminates the program, calling a custom terminate implementation if
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@ -1475,7 +1474,7 @@ namespace std
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// return.
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// return.
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abort();
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abort();
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}
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}
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terminateHandler.load()();
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terminateHandler();
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}
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}
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/**
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/**
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* Called when an unexpected exception is encountered (i.e. an exception
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* Called when an unexpected exception is encountered (i.e. an exception
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@ -1492,7 +1491,7 @@ namespace std
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// return.
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// return.
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abort();
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abort();
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}
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}
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unexpectedHandler.load()();
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unexpectedHandler();
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}
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}
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/**
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/**
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* Returns whether there are any exceptions currently being thrown that
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* Returns whether there are any exceptions currently being thrown that
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@ -1522,7 +1521,7 @@ namespace std
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{
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{
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return info->unexpectedHandler;
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return info->unexpectedHandler;
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}
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}
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return unexpectedHandler.load();
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return ATOMIC_LOAD(&unexpectedHandler);
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}
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}
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/**
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/**
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* Returns the current terminate handler.
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* Returns the current terminate handler.
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@ -1534,7 +1533,7 @@ namespace std
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{
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{
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return info->terminateHandler;
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return info->terminateHandler;
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}
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}
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return terminateHandler.load();
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return ATOMIC_LOAD(&terminateHandler);
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}
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}
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}
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}
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#if defined(__arm__) && !defined(__ARM_DWARF_EH__)
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#if defined(__arm__) && !defined(__ARM_DWARF_EH__)
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@ -1,6 +1,5 @@
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/*
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/*
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* Copyright 2010-2012 PathScale, Inc. All rights reserved.
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* Copyright 2010-2012 PathScale, Inc. All rights reserved.
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* Copyright 2021 David Chisnall. All rights reserved.
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*
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*
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* Redistribution and use in source and binary forms, with or without
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* modification, are permitted provided that the following conditions are met:
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@ -11,7 +10,7 @@
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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* and/or other materials provided with the distribution.
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*
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
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* IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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@ -39,305 +38,126 @@
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* value as a low-overhead lock. Because statics (in most sane code) are
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* value as a low-overhead lock. Because statics (in most sane code) are
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* accessed far more times than they are initialised, this lock implementation
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* accessed far more times than they are initialised, this lock implementation
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* is heavily optimised towards the case where the static has already been
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* is heavily optimised towards the case where the static has already been
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* initialised.
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* initialised.
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*/
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*/
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#include "atomic.h"
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#include <assert.h>
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#include <pthread.h>
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#include <stdint.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <pthread.h>
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#include <assert.h>
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#include "atomic.h"
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// Older GCC doesn't define __LITTLE_ENDIAN__
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// Older GCC doesn't define __LITTLE_ENDIAN__
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#ifndef __LITTLE_ENDIAN__
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#ifndef __LITTLE_ENDIAN__
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// If __BYTE_ORDER__ is defined, use that instead
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// If __BYTE_ORDER__ is defined, use that instead
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# ifdef __BYTE_ORDER__
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# ifdef __BYTE_ORDER__
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# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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# define __LITTLE_ENDIAN__
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# define __LITTLE_ENDIAN__
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# endif
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# endif
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// x86 and ARM are the most common little-endian CPUs, so let's have a
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// x86 and ARM are the most common little-endian CPUs, so let's have a
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// special case for them (ARM is already special cased). Assume everything
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// special case for them (ARM is already special cased). Assume everything
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// else is big endian.
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// else is big endian.
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# elif defined(__x86_64) || defined(__i386)
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# elif defined(__x86_64) || defined(__i386)
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# define __LITTLE_ENDIAN__
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# define __LITTLE_ENDIAN__
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# endif
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# endif
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#endif
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#endif
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/*
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/*
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* The Itanium C++ ABI defines guard words that are 64-bit (32-bit on AArch32)
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* The least significant bit of the guard variable indicates that the object
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* values with one bit defined to indicate that the guarded variable is and
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* has been initialised, the most significant bit is used for a spinlock.
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* another bit to indicate that it's currently locked (initialisation in
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* progress). The bit to use depends on the byte order of the target.
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*
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* On many 32-bit platforms, 64-bit atomics are unavailable (or slow) and so we
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* treat the two halves of the 64-bit word as independent values and
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*/
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*/
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namespace
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{
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/**
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* The state of the guard variable when an attempt is made to lock it.
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*/
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enum class GuardState
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{
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/**
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* The lock is not held but is not needed because initialisation is
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* one.
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*/
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InitDone,
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/**
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* Initialisation is not done but the lock is held by the caller.
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*/
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InitLockSucceeded,
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/**
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* Attempting to acquire the lock failed.
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*/
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InitLockFailed
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};
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/**
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* Class encapsulating a single atomic word being used to represent the
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* guard. The word size is defined by the type of `GuardWord`. The bit
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* used to indicate the locked state is `1<<LockedBit`, the bit used to
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* indicate the initialised state is `1<<InitBit`.
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*/
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template<typename GuardWord, int LockedBit, int InitBit>
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struct SingleWordGuard
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{
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/**
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* The value indicating that the lock bit is set (and no other bits).
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*/
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static constexpr GuardWord locked = static_cast<GuardWord>(1)
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<< LockedBit;
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/**
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* The value indicating that the initialised bit is set (and all other
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* bits are zero).
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*/
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static constexpr GuardWord initialised = static_cast<GuardWord>(1)
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<< InitBit;
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/**
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* The guard variable.
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*/
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atomic<GuardWord> val;
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public:
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/**
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* Release the lock and set the initialised state. In the single-word
|
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* implementation here, these are both done by a single store.
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*/
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void unlock(bool isInitialised)
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{
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val.store(isInitialised ? initialised : 0, memory_order::release);
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#ifndef NDEBUG
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GuardWord init_state = initialised;
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assert(*reinterpret_cast<uint8_t*>(&init_state) != 0);
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#endif
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}
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/**
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* Try to acquire the lock. This has a tri-state return, indicating
|
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* either that the lock was acquired, it wasn't acquired because it was
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* contended, or it wasn't acquired because the guarded variable is
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* already initialised.
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*/
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GuardState try_lock()
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{
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GuardWord old = 0;
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// Try to acquire the lock, assuming that we are in the state where
|
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// the lock is not held and the variable is not initialised (so the
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// expected value is 0).
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if (val.compare_exchange(old, locked))
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{
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return GuardState::InitLockSucceeded;
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}
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// If the CAS failed and the old value indicates that this is
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// initialised, return that initialisation is done and skip further
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// retries.
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if (old == initialised)
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{
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return GuardState::InitDone;
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}
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// Otherwise, report failure.
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return GuardState::InitLockFailed;
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}
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|
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/**
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* Check whether the guard indicates that the variable is initialised.
|
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*/
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bool is_initialised()
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{
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return (val.load(memory_order::acquire) & initialised) ==
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initialised;
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}
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};
|
|
||||||
|
|
||||||
/**
|
|
||||||
* Class encapsulating using two 32-bit atomic values to represent a 64-bit
|
|
||||||
* guard variable.
|
|
||||||
*/
|
|
||||||
template<int LockedBit, int InitBit>
|
|
||||||
class DoubleWordGuard
|
|
||||||
{
|
|
||||||
/**
|
|
||||||
* The value of `lock_word` when the lock is held.
|
|
||||||
*/
|
|
||||||
static constexpr uint32_t locked = static_cast<uint32_t>(1)
|
|
||||||
<< LockedBit;
|
|
||||||
|
|
||||||
/**
|
|
||||||
* The value of `init_word` when the guarded variable is initialised.
|
|
||||||
*/
|
|
||||||
static constexpr uint32_t initialised = static_cast<uint32_t>(1)
|
|
||||||
<< InitBit;
|
|
||||||
|
|
||||||
/**
|
|
||||||
* The word used for the initialised flag. This is always the first
|
|
||||||
* word irrespective of endian because the generated code compares the
|
|
||||||
* first byte in memory against 0.
|
|
||||||
*/
|
|
||||||
atomic<uint32_t> init_word;
|
|
||||||
|
|
||||||
/**
|
|
||||||
* The word used for the lock.
|
|
||||||
*/
|
|
||||||
atomic<uint32_t> lock_word;
|
|
||||||
|
|
||||||
public:
|
|
||||||
/**
|
|
||||||
* Try to acquire the lock. This has a tri-state return, indicating
|
|
||||||
* either that the lock was acquired, it wasn't acquired because it was
|
|
||||||
* contended, or it wasn't acquired because the guarded variable is
|
|
||||||
* already initialised.
|
|
||||||
*/
|
|
||||||
GuardState try_lock()
|
|
||||||
{
|
|
||||||
uint32_t old = 0;
|
|
||||||
// Try to acquire the lock
|
|
||||||
if (lock_word.compare_exchange(old, locked))
|
|
||||||
{
|
|
||||||
// If we succeeded, check if initialisation has happened. In
|
|
||||||
// this version, we don't have atomic manipulation of both the
|
|
||||||
// lock and initialised bits together. Instead, we have an
|
|
||||||
// ordering rule that the initialised bit is only ever updated
|
|
||||||
// with the lock held.
|
|
||||||
if (is_initialised())
|
|
||||||
{
|
|
||||||
// If another thread did manage to initialise this, release
|
|
||||||
// the lock and notify the caller that initialisation is
|
|
||||||
// done.
|
|
||||||
lock_word.store(initialised, memory_order::release);
|
|
||||||
return GuardState::InitDone;
|
|
||||||
}
|
|
||||||
return GuardState::InitLockSucceeded;
|
|
||||||
}
|
|
||||||
return GuardState::InitLockFailed;
|
|
||||||
}
|
|
||||||
|
|
||||||
/**
|
|
||||||
* Set the initialised state and release the lock. In this
|
|
||||||
* implementation, this is ordered, not atomic: the initialise bit is
|
|
||||||
* set while the lock is held.
|
|
||||||
*/
|
|
||||||
void unlock(bool isInitialised)
|
|
||||||
{
|
|
||||||
init_word.store(isInitialised ? initialised : 0,
|
|
||||||
memory_order::release);
|
|
||||||
lock_word.store(0, memory_order::release);
|
|
||||||
assert((*reinterpret_cast<uint8_t*>(this) != 0) == isInitialised);
|
|
||||||
}
|
|
||||||
|
|
||||||
/**
|
|
||||||
* Return whether the guarded variable is initialised.
|
|
||||||
*/
|
|
||||||
bool is_initialised()
|
|
||||||
{
|
|
||||||
return (init_word.load(memory_order::acquire) & initialised) ==
|
|
||||||
initialised;
|
|
||||||
}
|
|
||||||
};
|
|
||||||
|
|
||||||
// Check that the two implementations are the correct size.
|
|
||||||
static_assert(sizeof(SingleWordGuard<uint32_t, 31, 0>) == sizeof(uint32_t),
|
|
||||||
"Single-word 32-bit guard must be 32 bits");
|
|
||||||
static_assert(sizeof(SingleWordGuard<uint64_t, 63, 0>) == sizeof(uint64_t),
|
|
||||||
"Single-word 64-bit guard must be 64 bits");
|
|
||||||
static_assert(sizeof(DoubleWordGuard<31, 0>) == sizeof(uint64_t),
|
|
||||||
"Double-word guard must be 64 bits");
|
|
||||||
|
|
||||||
#ifdef __arm__
|
#ifdef __arm__
|
||||||
/**
|
// ARM ABI - 32-bit guards.
|
||||||
* The Arm PCS defines a variant of the Itanium ABI with 32-bit lock words.
|
typedef uint32_t guard_t;
|
||||||
*/
|
typedef uint32_t guard_lock_t;
|
||||||
using Guard = SingleWordGuard<uint32_t, 31, 0>;
|
static const uint32_t LOCKED = static_cast<guard_t>(1) << 31;
|
||||||
|
static const uint32_t INITIALISED = 1;
|
||||||
|
#define LOCK_PART(guard) (guard)
|
||||||
|
#define INIT_PART(guard) (guard)
|
||||||
#elif defined(_LP64)
|
#elif defined(_LP64)
|
||||||
|
typedef uint64_t guard_t;
|
||||||
|
typedef uint64_t guard_lock_t;
|
||||||
# if defined(__LITTLE_ENDIAN__)
|
# if defined(__LITTLE_ENDIAN__)
|
||||||
/**
|
static const guard_t LOCKED = static_cast<guard_t>(1) << 63;
|
||||||
* On little-endian 64-bit platforms the guard word is a single 64-bit
|
static const guard_t INITIALISED = 1;
|
||||||
* atomic with the lock in the high bit and the initialised flag in the low
|
|
||||||
* bit.
|
|
||||||
*/
|
|
||||||
using Guard = SingleWordGuard<uint64_t, 63, 0>;
|
|
||||||
# else
|
# else
|
||||||
/**
|
static const guard_t LOCKED = 1;
|
||||||
* On bit-endian 64-bit platforms, the guard word is a single 64-bit atomic
|
static const guard_t INITIALISED = static_cast<guard_t>(1) << 56;
|
||||||
* with the lock in the low bit and the initialised bit in the highest
|
|
||||||
* byte.
|
|
||||||
*/
|
|
||||||
using Guard = SingleWordGuard<uint64_t, 0, 56>;
|
|
||||||
# endif
|
# endif
|
||||||
|
#define LOCK_PART(guard) (guard)
|
||||||
|
#define INIT_PART(guard) (guard)
|
||||||
#else
|
#else
|
||||||
|
typedef uint32_t guard_lock_t;
|
||||||
# if defined(__LITTLE_ENDIAN__)
|
# if defined(__LITTLE_ENDIAN__)
|
||||||
/**
|
typedef struct {
|
||||||
* 32-bit platforms use the same layout as 64-bit.
|
uint32_t init_half;
|
||||||
*/
|
uint32_t lock_half;
|
||||||
using Guard = DoubleWordGuard<31, 0>;
|
} guard_t;
|
||||||
|
static const uint32_t LOCKED = static_cast<guard_lock_t>(1) << 31;
|
||||||
|
static const uint32_t INITIALISED = 1;
|
||||||
# else
|
# else
|
||||||
/**
|
typedef struct {
|
||||||
* 32-bit platforms use the same layout as 64-bit.
|
uint32_t init_half;
|
||||||
*/
|
uint32_t lock_half;
|
||||||
using Guard = DoubleWordGuard<0, 24>;
|
} guard_t;
|
||||||
|
static_assert(sizeof(guard_t) == sizeof(uint64_t), "");
|
||||||
|
static const uint32_t LOCKED = 1;
|
||||||
|
static const uint32_t INITIALISED = static_cast<guard_lock_t>(1) << 24;
|
||||||
# endif
|
# endif
|
||||||
|
#define LOCK_PART(guard) (&(guard)->lock_half)
|
||||||
|
#define INIT_PART(guard) (&(guard)->init_half)
|
||||||
#endif
|
#endif
|
||||||
|
static const guard_lock_t INITIAL = 0;
|
||||||
} // namespace
|
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Acquires a lock on a guard, returning 0 if the object has already been
|
* Acquires a lock on a guard, returning 0 if the object has already been
|
||||||
* initialised, and 1 if it has not. If the object is already constructed then
|
* initialised, and 1 if it has not. If the object is already constructed then
|
||||||
* this function just needs to read a byte from memory and return.
|
* this function just needs to read a byte from memory and return.
|
||||||
*/
|
*/
|
||||||
extern "C" int __cxa_guard_acquire(Guard *guard_object)
|
extern "C" int __cxa_guard_acquire(volatile guard_t *guard_object)
|
||||||
{
|
{
|
||||||
// Check if this is already initialised. If so, we don't have to do
|
guard_lock_t old;
|
||||||
// anything.
|
// Not an atomic read, doesn't establish a happens-before relationship, but
|
||||||
if (guard_object->is_initialised())
|
// if one is already established and we end up seeing an initialised state
|
||||||
{
|
// then it's a fast path, otherwise we'll do something more expensive than
|
||||||
|
// this test anyway...
|
||||||
|
if (INITIALISED == *INIT_PART(guard_object))
|
||||||
return 0;
|
return 0;
|
||||||
}
|
// Spin trying to do the initialisation
|
||||||
// Spin trying to acquire the lock. If we fail to acquire the lock the
|
|
||||||
// first time then another thread will *probably* initialise it, but if the
|
|
||||||
// constructor throws an exception then we may have to try again in this
|
|
||||||
// thread.
|
|
||||||
for (;;)
|
for (;;)
|
||||||
{
|
{
|
||||||
// Try to acquire the lock.
|
// Loop trying to move the value of the guard from 0 (not
|
||||||
switch (guard_object->try_lock())
|
// locked, not initialised) to the locked-uninitialised
|
||||||
{
|
// position.
|
||||||
// If we failed to acquire the lock but another thread has
|
old = __sync_val_compare_and_swap(LOCK_PART(guard_object),
|
||||||
// initialised the lock while we were waiting, return immediately
|
INITIAL, LOCKED);
|
||||||
// indicating that initialisation is not required.
|
if (old == INITIAL) {
|
||||||
case GuardState::InitDone:
|
// Lock obtained. If lock and init bit are
|
||||||
return 0;
|
// in separate words, check for init race.
|
||||||
// If we acquired the lock, return immediately to start
|
if (INIT_PART(guard_object) == LOCK_PART(guard_object))
|
||||||
// initialisation.
|
|
||||||
case GuardState::InitLockSucceeded:
|
|
||||||
return 1;
|
return 1;
|
||||||
// If we didn't acquire the lock, pause and retry.
|
if (INITIALISED != *INIT_PART(guard_object))
|
||||||
case GuardState::InitLockFailed:
|
return 1;
|
||||||
break;
|
|
||||||
|
// No need for a memory barrier here,
|
||||||
|
// see first comment.
|
||||||
|
*LOCK_PART(guard_object) = INITIAL;
|
||||||
|
return 0;
|
||||||
}
|
}
|
||||||
|
// If lock and init bit are in the same word, check again
|
||||||
|
// if we are done.
|
||||||
|
if (INIT_PART(guard_object) == LOCK_PART(guard_object) &&
|
||||||
|
old == INITIALISED)
|
||||||
|
return 0;
|
||||||
|
|
||||||
|
assert(old == LOCKED);
|
||||||
|
// Another thread holds the lock.
|
||||||
|
// If lock and init bit are in different words, check
|
||||||
|
// if we are done before yielding and looping.
|
||||||
|
if (INIT_PART(guard_object) != LOCK_PART(guard_object) &&
|
||||||
|
INITIALISED == *INIT_PART(guard_object))
|
||||||
|
return 0;
|
||||||
sched_yield();
|
sched_yield();
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
@ -346,16 +166,28 @@ extern "C" int __cxa_guard_acquire(Guard *guard_object)
|
|||||||
* Releases the lock without marking the object as initialised. This function
|
* Releases the lock without marking the object as initialised. This function
|
||||||
* is called if initialising a static causes an exception to be thrown.
|
* is called if initialising a static causes an exception to be thrown.
|
||||||
*/
|
*/
|
||||||
extern "C" void __cxa_guard_abort(Guard *guard_object)
|
extern "C" void __cxa_guard_abort(volatile guard_t *guard_object)
|
||||||
{
|
{
|
||||||
guard_object->unlock(false);
|
__attribute__((unused))
|
||||||
|
bool reset = __sync_bool_compare_and_swap(LOCK_PART(guard_object),
|
||||||
|
LOCKED, INITIAL);
|
||||||
|
assert(reset);
|
||||||
}
|
}
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Releases the guard and marks the object as initialised. This function is
|
* Releases the guard and marks the object as initialised. This function is
|
||||||
* called after successful initialisation of a static.
|
* called after successful initialisation of a static.
|
||||||
*/
|
*/
|
||||||
extern "C" void __cxa_guard_release(Guard *guard_object)
|
extern "C" void __cxa_guard_release(volatile guard_t *guard_object)
|
||||||
{
|
{
|
||||||
guard_object->unlock(true);
|
guard_lock_t old;
|
||||||
|
if (INIT_PART(guard_object) == LOCK_PART(guard_object))
|
||||||
|
old = LOCKED;
|
||||||
|
else
|
||||||
|
old = INITIAL;
|
||||||
|
__attribute__((unused))
|
||||||
|
bool reset = __sync_bool_compare_and_swap(INIT_PART(guard_object),
|
||||||
|
old, INITIALISED);
|
||||||
|
assert(reset);
|
||||||
|
if (INIT_PART(guard_object) != LOCK_PART(guard_object))
|
||||||
|
*LOCK_PART(guard_object) = INITIAL;
|
||||||
}
|
}
|
||||||
|
@ -51,7 +51,7 @@ typedef void (*new_handler)();
|
|||||||
* The function to call when allocation fails. By default, there is no
|
* The function to call when allocation fails. By default, there is no
|
||||||
* handler and a bad allocation exception is thrown if an allocation fails.
|
* handler and a bad allocation exception is thrown if an allocation fails.
|
||||||
*/
|
*/
|
||||||
static atomic<new_handler> new_handl{nullptr};
|
static new_handler new_handl;
|
||||||
|
|
||||||
namespace std
|
namespace std
|
||||||
{
|
{
|
||||||
@ -61,13 +61,12 @@ namespace std
|
|||||||
__attribute__((weak))
|
__attribute__((weak))
|
||||||
new_handler set_new_handler(new_handler handler)
|
new_handler set_new_handler(new_handler handler)
|
||||||
{
|
{
|
||||||
return new_handl.exchange(handler);
|
return ATOMIC_SWAP(&new_handl, handler);
|
||||||
}
|
}
|
||||||
|
|
||||||
__attribute__((weak))
|
__attribute__((weak))
|
||||||
new_handler get_new_handler(void)
|
new_handler get_new_handler(void)
|
||||||
{
|
{
|
||||||
return new_handl.load();
|
return ATOMIC_LOAD(&new_handl);
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
Loading…
Reference in New Issue
Block a user