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mfbt/ThreadLocal.h@97036ab72558 (annotated)

mfbt/ThreadLocal.h

Tue, 06 Jan 2015 21:39:09 +0100

author

Michael Schloh von Bennewitz <michael@schloh.com>

date

Tue, 06 Jan 2015 21:39:09 +0100

branch

TOR_BUG_9701

changeset 8

97036ab72558

permissions

-rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

michael@0	1	/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0	2	/* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0	3	/* This Source Code Form is subject to the terms of the Mozilla Public
michael@0	4	* License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0	5	* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0	6
michael@0	7	/* Cross-platform lightweight thread local data wrappers. */
michael@0	8
michael@0	9	#ifndef mozilla_ThreadLocal_h
michael@0	10	#define mozilla_ThreadLocal_h
michael@0	11
michael@0	12	#if defined(XP_WIN)
michael@0	13	// This file will get included in any file that wants to add a profiler mark.
michael@0	14	// In order to not bring <windows.h> together we could include windef.h and
michael@0	15	// winbase.h which are sufficient to get the prototypes for the Tls* functions.
michael@0	16	// # include <windef.h>
michael@0	17	// # include <winbase.h>
michael@0	18	// Unfortunately, even including these headers causes us to add a bunch of ugly
michael@0	19	// stuff to our namespace e.g #define CreateEvent CreateEventW
michael@0	20	extern "C" {
michael@0	21	__declspec(dllimport) void* __stdcall TlsGetValue(unsigned long);
michael@0	22	__declspec(dllimport) int __stdcall TlsSetValue(unsigned long, void*);
michael@0	23	__declspec(dllimport) unsigned long __stdcall TlsAlloc();
michael@0	24	}
michael@0	25	#else
michael@0	26	# include <pthread.h>
michael@0	27	# include <signal.h>
michael@0	28	#endif
michael@0	29
michael@0	30	#include "mozilla/Assertions.h"
michael@0	31	#include "mozilla/Attributes.h"
michael@0	32	#include "mozilla/NullPtr.h"
michael@0	33
michael@0	34	namespace mozilla {
michael@0	35
michael@0	36	// sig_safe_t denotes an atomic type which can be read or stored in a single
michael@0	37	// instruction. This means that data of this type is safe to be manipulated
michael@0	38	// from a signal handler, or other similar asynchronous execution contexts.
michael@0	39	#if defined(XP_WIN)
michael@0	40	typedef unsigned long sig_safe_t;
michael@0	41	#else
michael@0	42	typedef sig_atomic_t sig_safe_t;
michael@0	43	#endif
michael@0	44
michael@0	45	/*
michael@0	46	* Thread Local Storage helpers.
michael@0	47	*
michael@0	48	* Usage:
michael@0	49	*
michael@0	50	* Only static-storage-duration (e.g. global variables, or static class members)
michael@0	51	* objects of this class should be instantiated. This class relies on
michael@0	52	* zero-initialization, which is implicit for static-storage-duration objects.
michael@0	53	* It doesn't have a custom default constructor, to avoid static initializers.
michael@0	54	*
michael@0	55	* API usage:
michael@0	56	*
michael@0	57	* // Create a TLS item.
michael@0	58	* //
michael@0	59	* // Note that init() should be invoked exactly once, before any usage of set()
michael@0	60	* // or get().
michael@0	61	* mozilla::ThreadLocal<int> tlsKey;
michael@0	62	* if (!tlsKey.init()) {
michael@0	63	* // deal with the error
michael@0	64	* }
michael@0	65	*
michael@0	66	* // Set the TLS value
michael@0	67	* tlsKey.set(123);
michael@0	68	*
michael@0	69	* // Get the TLS value
michael@0	70	* int value = tlsKey.get();
michael@0	71	*/
michael@0	72	template<typename T>
michael@0	73	class ThreadLocal
michael@0	74	{
michael@0	75	#if defined(XP_WIN)
michael@0	76	typedef unsigned long key_t;
michael@0	77	#else
michael@0	78	typedef pthread_key_t key_t;
michael@0	79	#endif
michael@0	80
michael@0	81	union Helper {
michael@0	82	void* ptr;
michael@0	83	T value;
michael@0	84	};
michael@0	85
michael@0	86	public:
michael@0	87	MOZ_WARN_UNUSED_RESULT inline bool init();
michael@0	88
michael@0	89	inline T get() const;
michael@0	90
michael@0	91	inline void set(const T value);
michael@0	92
michael@0	93	bool initialized() const {
michael@0	94	return inited;
michael@0	95	}
michael@0	96
michael@0	97	private:
michael@0	98	key_t key;
michael@0	99	bool inited;
michael@0	100	};
michael@0	101
michael@0	102	template<typename T>
michael@0	103	inline bool
michael@0	104	ThreadLocal<T>::init()
michael@0	105	{
michael@0	106	static_assert(sizeof(T) <= sizeof(void*),
michael@0	107	"mozilla::ThreadLocal can't be used for types larger than "
michael@0	108	"a pointer");
michael@0	109	MOZ_ASSERT(!initialized());
michael@0	110	#ifdef XP_WIN
michael@0	111	key = TlsAlloc();
michael@0	112	inited = key != 0xFFFFFFFFUL; // TLS_OUT_OF_INDEXES
michael@0	113	#else
michael@0	114	inited = !pthread_key_create(&key, nullptr);
michael@0	115	#endif
michael@0	116	return inited;
michael@0	117	}
michael@0	118
michael@0	119	template<typename T>
michael@0	120	inline T
michael@0	121	ThreadLocal<T>::get() const
michael@0	122	{
michael@0	123	MOZ_ASSERT(initialized());
michael@0	124	Helper h;
michael@0	125	#ifdef XP_WIN
michael@0	126	h.ptr = TlsGetValue(key);
michael@0	127	#else
michael@0	128	h.ptr = pthread_getspecific(key);
michael@0	129	#endif
michael@0	130	return h.value;
michael@0	131	}
michael@0	132
michael@0	133	template<typename T>
michael@0	134	inline void
michael@0	135	ThreadLocal<T>::set(const T value)
michael@0	136	{
michael@0	137	MOZ_ASSERT(initialized());
michael@0	138	Helper h;
michael@0	139	h.value = value;
michael@0	140	bool succeeded;
michael@0	141	#ifdef XP_WIN
michael@0	142	succeeded = TlsSetValue(key, h.ptr);
michael@0	143	#else
michael@0	144	succeeded = !pthread_setspecific(key, h.ptr);
michael@0	145	#endif
michael@0	146	if (!succeeded)
michael@0	147	MOZ_CRASH();
michael@0	148	}
michael@0	149
michael@0	150	} // namespace mozilla
michael@0	151
michael@0	152	#endif /* mozilla_ThreadLocal_h */