Add algorithm/multiple_shared_lock.hpp.

6 files changed, 111 insertions, 1 deletions

diff --git a/Doxyfile b/Doxyfile
index 5e8a7b2f..91028ed7 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -765,7 +765,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = include/boost/afio/v2 release_notes.md
+INPUT                  = include/boost/afio/v2 include/boost/afio/v2/algorithm release_notes.md
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses
diff --git a/build/afio_v2.vcxproj b/build/afio_v2.vcxproj
index 01003978..45e1ee51 100644
--- a/build/afio_v2.vcxproj
+++ b/build/afio_v2.vcxproj
@@ -28,6 +28,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\include\boost\afio\v2\afio.hpp" />
+    <ClInclude Include="..\include\boost\afio\v2\algorithm\multiple_shared_lock.hpp" />
     <ClInclude Include="..\include\boost\afio\v2\async_file_handle.hpp" />
     <ClInclude Include="..\include\boost\afio\v2\config.hpp" />
     <ClInclude Include="..\include\boost\afio\v2\deadline.h" />
diff --git a/build/afio_v2.vcxproj.filters b/build/afio_v2.vcxproj.filters
index 712ac9ac..63cd46c0 100644
--- a/build/afio_v2.vcxproj.filters
+++ b/build/afio_v2.vcxproj.filters
@@ -16,6 +16,9 @@
     <Filter Include="src\windows">
       <UniqueIdentifier>{1df00b33-25a0-48b7-9246-595e32c0b58e}</UniqueIdentifier>
     </Filter>
+    <Filter Include="include\algorithm">
+      <UniqueIdentifier>{fc296930-fe1b-408e-be8f-bc9b8b27bd4b}</UniqueIdentifier>
+    </Filter>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\include\boost\afio\v2\afio.hpp">
@@ -60,6 +63,9 @@
     <ClInclude Include="..\include\boost\afio\v2\detail\impl\windows\import.hpp">
       <Filter>src\windows</Filter>
     </ClInclude>
+    <ClInclude Include="..\include\boost\afio\v2\algorithm\multiple_shared_lock.hpp">
+      <Filter>include\algorithm</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <None Include="..\include\boost\afio\v2\detail\impl\storage_profile.ipp">
diff --git a/include/boost/afio/v2/afio.hpp b/include/boost/afio/v2/afio.hpp
index 1cd1ef04..6d32964f 100644
--- a/include/boost/afio/v2/afio.hpp
+++ b/include/boost/afio/v2/afio.hpp
@@ -2,4 +2,6 @@
 #include "statfs.hpp"
 #include "storage_profile.hpp"
 
+#include "algorithm/multiple_shared_lock.hpp"
+
 #include "detail/child_process.hpp"
diff --git a/include/boost/afio/v2/algorithm/multiple_shared_lock.hpp b/include/boost/afio/v2/algorithm/multiple_shared_lock.hpp
new file mode 100644
index 00000000..4908b5be
--- /dev/null
+++ b/include/boost/afio/v2/algorithm/multiple_shared_lock.hpp
@@ -0,0 +1,97 @@
+/* multiple_shared_lock.hpp
+Efficient many actor read-write lock
+(C) 2016 Niall Douglas http://www.nedprod.com/
+File Created: March 2016
+
+
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef BOOST_AFIO_MULTIPLE_SHARED_LOCK_HPP
+#define BOOST_AFIO_MULTIPLE_SHARED_LOCK_HPP
+
+#include "../file_handle.hpp"
+
+BOOST_AFIO_V2_NAMESPACE_BEGIN
+
+namespace algorithm
+{
+  /*! \class multiple_shared_lock
+  \brief Efficient many actor shared/exclusive file system based lock
+
+  Lock files scale poorly to the number of items being concurrently locked with typically an exponential
+  drop off in performance as the number of items being concurrently locked rises. This file system
+  algorithm solves this problem using IPC via a shared append-only lock file.
+
+  - Compatible with networked file systems (NFS too if the special nfs_compatibility flag is true).
+  - Invariant complexity to number of items being locked.
+  - Linear complexity to number of processes concurrently using the lock (i.e. number of waiters).
+
+  Caveats:
+  - Wasteful of disk space if used on a non-extents based filing system (e.g. FAT32, ext3).
+  It is best used in `/tmp` if possible. If you really must use a non-extents based filing
+  system, destroy and recreate the object instance periodically to force resetting the lock
+  file's length to zero.
+  - Similarly older operating systems (e.g. Linux < 3.0) do not implement extent hole punching
+  and therefore will also see excessive disk space consumption. Note at the time of writing
+  OS X doesn't implement hole punching at all.
+  - Byte range locks need to work properly on your system. Misconfiguring NFS or Samba
+  to cause byte range locks to not work right will produce bad outcomes.
+  - If your OS doesn't have sane byte range locks (OS X, BSD, older Linuxes) and multiple
+  threads in your process use the same lock file, bad things will happen due to the lack
+  of sanity in POSIX byte range locks. This may get fixed with a process-local byte range
+  lock implementation if there is demand, otherwise simply don't use the same lock file
+  from more than one thread on such systems.
+  */
+
+  class multiple_shared_lock
+  {
+    file_handle _h;
+
+  public:
+    multiple_shared_lock() {}
+    multiple_shared_lock(const multiple_shared_lock &) = delete;
+    multiple_shared_lock &operator=(const multiple_shared_lock &) = delete;
+    multiple_shared_lock(multiple_shared_lock &&o) noexcept : _h(std::move(o._h)) {}
+    multiple_shared_lock &operator=(multiple_shared_lock &&o) noexcept
+    {
+      _h = std::move(o._h);
+      return *this;
+    }
+
+    static result<multiple_shared_lock> init(file_handle::path_type lockfile) noexcept {}
+
+    void lock();
+    bool try_lock();
+    result<void> try_lock_timed(deadline d);
+    void unlock();
+  };
+
+}  // namespace
+
+BOOST_AFIO_V2_NAMESPACE_END
+
+
+#endif
diff --git a/include/boost/afio/v2/config.hpp b/include/boost/afio/v2/config.hpp
index e9a3acf1..d73f015f 100644
--- a/include/boost/afio/v2/config.hpp
+++ b/include/boost/afio/v2/config.hpp
@@ -153,6 +153,10 @@ namespace boost
     //! Inline namespace for this version of AFIO
     inline namespace v2
     {
+      //! Collection of file system based algorithms
+      namespace algorithm
+      {
+      }
     }
   }
 }