Revert of Remove remains of webrtc/base (patchset #7 id:120001 of https://codereview.webrtc.org/297…

webrtc/base/sigslot.h

+// sigslot.h: Signal/Slot classes
+//
+// Written by Sarah Thompson (sarah@telergy.com) 2002.
+//
+// License: Public domain. You are free to use this code however you like, with
+// the proviso that the author takes on no responsibility or liability for any
+// use.
+//
+// QUICK DOCUMENTATION
+//
+//        (see also the full documentation at http://sigslot.sourceforge.net/)
+//
+//    #define switches
+//      SIGSLOT_PURE_ISO:
+//        Define this to force ISO C++ compliance. This also disables all of
+//        the thread safety support on platforms where it is available.
+//
+//      SIGSLOT_USE_POSIX_THREADS:
+//        Force use of Posix threads when using a C++ compiler other than gcc
+//        on a platform that supports Posix threads. (When using gcc, this is
+//        the default - use SIGSLOT_PURE_ISO to disable this if necessary)
+//
+//      SIGSLOT_DEFAULT_MT_POLICY:
+//        Where thread support is enabled, this defaults to
+//        multi_threaded_global. Otherwise, the default is single_threaded.
+//        #define this yourself to override the default. In pure ISO mode,
+//        anything other than single_threaded will cause a compiler error.
+//
+//    PLATFORM NOTES
+//
+//      Win32:
+//        On Win32, the WEBRTC_WIN symbol must be #defined. Most mainstream
+//        compilers do this by default, but you may need to define it yourself
+//        if your build environment is less standard. This causes the Win32
+//        thread support to be compiled in and used automatically.
+//
+//      Unix/Linux/BSD, etc.:
+//        If you're using gcc, it is assumed that you have Posix threads
+//        available, so they are used automatically. You can override this (as
+//        under Windows) with the SIGSLOT_PURE_ISO switch. If you're using
+//        something other than gcc but still want to use Posix threads, you
+//        need to #define SIGSLOT_USE_POSIX_THREADS.
+//
+//      ISO C++:
+//        If none of the supported platforms are detected, or if
+//        SIGSLOT_PURE_ISO is defined, all multithreading support is turned
+//        off, along with any code that might cause a pure ISO C++ environment
+//        to complain. Before you ask, gcc -ansi -pedantic won't compile this
+//        library, but gcc -ansi is fine. Pedantic mode seems to throw a lot of
+//        errors that aren't really there. If you feel like investigating this,
+//        please contact the author.
+//
+//
+//    THREADING MODES
+//
+//      single_threaded:
+//        Your program is assumed to be single threaded from the point of view
+//        of signal/slot usage (i.e. all objects using signals and slots are
+//        created and destroyed from a single thread). Behaviour if objects are
+//        destroyed concurrently is undefined (i.e. you'll get the occasional
+//        segmentation fault/memory exception).
+//
+//      multi_threaded_global:
+//        Your program is assumed to be multi threaded. Objects using signals
+//        and slots can be safely created and destroyed from any thread, even
+//        when connections exist. In multi_threaded_global mode, this is
+//        achieved by a single global mutex (actually a critical section on
+//        Windows because they are faster). This option uses less OS resources,
+//        but results in more opportunities for contention, possibly resulting
+//        in more context switches than are strictly necessary.
+//
+//      multi_threaded_local:
+//        Behaviour in this mode is essentially the same as
+//        multi_threaded_global, except that each signal, and each object that
+//        inherits has_slots, all have their own mutex/critical section. In
+//        practice, this means that mutex collisions (and hence context
+//        switches) only happen if they are absolutely essential. However, on
+//        some platforms, creating a lot of mutexes can slow down the whole OS,
+//        so use this option with care.
+//
+//    USING THE LIBRARY
+//
+//      See the full documentation at http://sigslot.sourceforge.net/
+//
+// Libjingle specific:
+//
+// This file has been modified such that has_slots and signalx do not have to be
+// using the same threading requirements. E.g. it is possible to connect a
+// has_slots<single_threaded> and signal0<multi_threaded_local> or
+// has_slots<multi_threaded_local> and signal0<single_threaded>.
+// If has_slots is single threaded the user must ensure that it is not trying
+// to connect or disconnect to signalx concurrently or data race may occur.
+// If signalx is single threaded the user must ensure that disconnect, connect
+// or signal is not happening concurrently or data race may occur.
+
+#ifndef WEBRTC_BASE_SIGSLOT_H_
+#define WEBRTC_BASE_SIGSLOT_H_
+
+
+// This header is deprecated and is just left here temporarily during
+// refactoring. See https://bugs.webrtc.org/7634 for more details.
+#include "webrtc/rtc_base/sigslot.h"
+
+#endif  // WEBRTC_BASE_SIGSLOT_H_