The Tor Browser: mfbt/ThreadLocal.h@97036ab72558

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.

     1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */

     3 /* This Source Code Form is subject to the terms of the Mozilla Public

     4  * License, v. 2.0. If a copy of the MPL was not distributed with this

     5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     7 /* Cross-platform lightweight thread local data wrappers. */

     9 #ifndef mozilla_ThreadLocal_h

    10 #define mozilla_ThreadLocal_h

    12 #if defined(XP_WIN)

    13 // This file will get included in any file that wants to add a profiler mark.

    14 // In order to not bring <windows.h> together we could include windef.h and

    15 // winbase.h which are sufficient to get the prototypes for the Tls* functions.

    16 // # include <windef.h>

    17 // # include <winbase.h>

    18 // Unfortunately, even including these headers causes us to add a bunch of ugly

    19 // stuff to our namespace e.g #define CreateEvent CreateEventW

    20 extern "C" {

    21 __declspec(dllimport) void* __stdcall TlsGetValue(unsigned long);

    22 __declspec(dllimport) int __stdcall TlsSetValue(unsigned long, void*);

    23 __declspec(dllimport) unsigned long __stdcall TlsAlloc();

    24 }

    25 #else

    26 #  include <pthread.h>

    27 #  include <signal.h>

    28 #endif

    30 #include "mozilla/Assertions.h"

    31 #include "mozilla/Attributes.h"

    32 #include "mozilla/NullPtr.h"

    34 namespace mozilla {

    36 // sig_safe_t denotes an atomic type which can be read or stored in a single

    37 // instruction.  This means that data of this type is safe to be manipulated

    38 // from a signal handler, or other similar asynchronous execution contexts.

    39 #if defined(XP_WIN)

    40 typedef unsigned long sig_safe_t;

    41 #else

    42 typedef sig_atomic_t sig_safe_t;

    43 #endif

    45 /*

    46  * Thread Local Storage helpers.

    47  *

    48  * Usage:

    49  *

    50  * Only static-storage-duration (e.g. global variables, or static class members)

    51  * objects of this class should be instantiated. This class relies on

    52  * zero-initialization, which is implicit for static-storage-duration objects.

    53  * It doesn't have a custom default constructor, to avoid static initializers.

    54  *

    55  * API usage:

    56  *

    57  * // Create a TLS item.

    58  * //

    59  * // Note that init() should be invoked exactly once, before any usage of set()

    60  * // or get().

    61  * mozilla::ThreadLocal<int> tlsKey;

    62  * if (!tlsKey.init()) {

    63  *   // deal with the error

    64  * }

    65  *

    66  * // Set the TLS value

    67  * tlsKey.set(123);

    68  *

    69  * // Get the TLS value

    70  * int value = tlsKey.get();

    71  */

    72 template<typename T>

    73 class ThreadLocal

    74 {

    75 #if defined(XP_WIN)

    76     typedef unsigned long key_t;

    77 #else

    78     typedef pthread_key_t key_t;

    79 #endif

    81     union Helper {

    82       void* ptr;

    83       T value;

    84     };

    86   public:

    87     MOZ_WARN_UNUSED_RESULT inline bool init();

    89     inline T get() const;

    91     inline void set(const T value);

    93     bool initialized() const {

    94       return inited;

    95     }

    97   private:

    98     key_t key;

    99     bool inited;

   100 };

   102 template<typename T>

   103 inline bool

   104 ThreadLocal<T>::init()

   105 {

   106   static_assert(sizeof(T) <= sizeof(void*),

   107                 "mozilla::ThreadLocal can't be used for types larger than "

   108                 "a pointer");

   109   MOZ_ASSERT(!initialized());

   110 #ifdef XP_WIN

   111   key = TlsAlloc();

   112   inited = key != 0xFFFFFFFFUL; // TLS_OUT_OF_INDEXES

   113 #else

   114   inited = !pthread_key_create(&key, nullptr);

   115 #endif

   116   return inited;

   117 }

   119 template<typename T>

   120 inline T

   121 ThreadLocal<T>::get() const

   122 {

   123   MOZ_ASSERT(initialized());

   124   Helper h;

   125 #ifdef XP_WIN

   126   h.ptr = TlsGetValue(key);

   127 #else

   128   h.ptr = pthread_getspecific(key);

   129 #endif

   130   return h.value;

   131 }

   133 template<typename T>

   134 inline void

   135 ThreadLocal<T>::set(const T value)

   136 {

   137   MOZ_ASSERT(initialized());

   138   Helper h;

   139   h.value = value;

   140   bool succeeded;

   141 #ifdef XP_WIN

   142   succeeded = TlsSetValue(key, h.ptr);

   143 #else

   144   succeeded = !pthread_setspecific(key, h.ptr);

   145 #endif

   146   if (!succeeded)

   147     MOZ_CRASH();

   148 }

   150 } // namespace mozilla

   152 #endif /* mozilla_ThreadLocal_h */

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mfbt/ThreadLocal.h@97036ab72558

mfbt/ThreadLocal.h