cannam@149: // Copyright (c) 2014, Jason Choy <jjwchoy@gmail.com>
cannam@149: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
cannam@149: // Licensed under the MIT License:
cannam@149: //
cannam@149: // Permission is hereby granted, free of charge, to any person obtaining a copy
cannam@149: // of this software and associated documentation files (the "Software"), to deal
cannam@149: // in the Software without restriction, including without limitation the rights
cannam@149: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
cannam@149: // copies of the Software, and to permit persons to whom the Software is
cannam@149: // furnished to do so, subject to the following conditions:
cannam@149: //
cannam@149: // The above copyright notice and this permission notice shall be included in
cannam@149: // all copies or substantial portions of the Software.
cannam@149: //
cannam@149: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
cannam@149: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
cannam@149: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
cannam@149: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
cannam@149: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
cannam@149: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
cannam@149: // THE SOFTWARE.
cannam@149: 
cannam@149: #ifndef KJ_THREADLOCAL_H_
cannam@149: #define KJ_THREADLOCAL_H_
cannam@149: 
cannam@149: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
cannam@149: #pragma GCC system_header
cannam@149: #endif
cannam@149: // This file declares a macro `KJ_THREADLOCAL_PTR` for declaring thread-local pointer-typed
cannam@149: // variables.  Use like:
cannam@149: //     KJ_THREADLOCAL_PTR(MyType) foo = nullptr;
cannam@149: // This is equivalent to:
cannam@149: //     thread_local MyType* foo = nullptr;
cannam@149: // This can only be used at the global scope.
cannam@149: //
cannam@149: // AVOID USING THIS.  Use of thread-locals is discouraged because they often have many of the same
cannam@149: // properties as singletons: http://www.object-oriented-security.org/lets-argue/singletons
cannam@149: //
cannam@149: // Also, thread-locals tend to be hostile to event-driven code, which can be particularly
cannam@149: // surprising when using fibers (all fibers in the same thread will share the same threadlocals,
cannam@149: // even though they do not share a stack).
cannam@149: //
cannam@149: // That said, thread-locals are sometimes needed for runtime logistics in the KJ framework.  For
cannam@149: // example, the current exception callback and current EventLoop are stored as thread-local
cannam@149: // pointers.  Since KJ only ever needs to store pointers, not values, we avoid the question of
cannam@149: // whether these values' destructors need to be run, and we avoid the need for heap allocation.
cannam@149: 
cannam@149: #include "common.h"
cannam@149: 
cannam@149: #if !defined(KJ_USE_PTHREAD_THREADLOCAL) && defined(__APPLE__)
cannam@149: #include "TargetConditionals.h"
cannam@149: #if TARGET_OS_IPHONE
cannam@149: // iOS apparently does not support __thread (nor C++11 thread_local).
cannam@149: #define KJ_USE_PTHREAD_TLS 1
cannam@149: #endif
cannam@149: #endif
cannam@149: 
cannam@149: #if KJ_USE_PTHREAD_TLS
cannam@149: #include <pthread.h>
cannam@149: #endif
cannam@149: 
cannam@149: namespace kj {
cannam@149: 
cannam@149: #if KJ_USE_PTHREAD_TLS
cannam@149: // If __thread is unavailable, we'll fall back to pthreads.
cannam@149: 
cannam@149: #define KJ_THREADLOCAL_PTR(type) \
cannam@149:   namespace { struct KJ_UNIQUE_NAME(_kj_TlpTag); } \
cannam@149:   static ::kj::_::ThreadLocalPtr< type, KJ_UNIQUE_NAME(_kj_TlpTag)>
cannam@149: // Hack:  In order to ensure each thread-local results in a unique template instance, we declare
cannam@149: //   a one-off dummy type to use as the second type parameter.
cannam@149: 
cannam@149: namespace _ {  // private
cannam@149: 
cannam@149: template <typename T, typename>
cannam@149: class ThreadLocalPtr {
cannam@149:   // Hacky type to emulate __thread T*.  We need a separate instance of the ThreadLocalPtr template
cannam@149:   // for every thread-local variable, because we don't want to require a global constructor, and in
cannam@149:   // order to initialize the TLS on first use we need to use a local static variable (in getKey()).
cannam@149:   // Each template instance will get a separate such local static variable, fulfilling our need.
cannam@149: 
cannam@149: public:
cannam@149:   ThreadLocalPtr() = default;
cannam@149:   constexpr ThreadLocalPtr(decltype(nullptr)) {}
cannam@149:   // Allow initialization to nullptr without a global constructor.
cannam@149: 
cannam@149:   inline ThreadLocalPtr& operator=(T* val) {
cannam@149:     pthread_setspecific(getKey(), val);
cannam@149:     return *this;
cannam@149:   }
cannam@149: 
cannam@149:   inline operator T*() const {
cannam@149:     return get();
cannam@149:   }
cannam@149: 
cannam@149:   inline T& operator*() const {
cannam@149:     return *get();
cannam@149:   }
cannam@149: 
cannam@149:   inline T* operator->() const {
cannam@149:     return get();
cannam@149:   }
cannam@149: 
cannam@149: private:
cannam@149:   inline T* get() const {
cannam@149:     return reinterpret_cast<T*>(pthread_getspecific(getKey()));
cannam@149:   }
cannam@149: 
cannam@149:   inline static pthread_key_t getKey() {
cannam@149:     static pthread_key_t key = createKey();
cannam@149:     return key;
cannam@149:   }
cannam@149: 
cannam@149:   static pthread_key_t createKey() {
cannam@149:     pthread_key_t key;
cannam@149:     pthread_key_create(&key, 0);
cannam@149:     return key;
cannam@149:   }
cannam@149: };
cannam@149: 
cannam@149: }  // namespace _ (private)
cannam@149: 
cannam@149: #elif __GNUC__
cannam@149: 
cannam@149: #define KJ_THREADLOCAL_PTR(type) static __thread type*
cannam@149: // GCC's __thread is lighter-weight than thread_local and is good enough for our purposes.
cannam@149: 
cannam@149: #else
cannam@149: 
cannam@149: #define KJ_THREADLOCAL_PTR(type) static thread_local type*
cannam@149: 
cannam@149: #endif // KJ_USE_PTHREAD_TLS
cannam@149: 
cannam@149: }  // namespace kj
cannam@149: 
cannam@149: #endif  // KJ_THREADLOCAL_H_