Enhance soft lock

Author: javalikescript

jls/lang/Lock-.lua

@@ -1,11 +1,73 @@
 local class = require('jls.lang.class')
+local system = require('jls.lang.system')
+
+local function read(file, offset)
+  file:seek('set', offset)
+  local s = file:read(1)
+  if s then
+    return (string.byte(s))
+  end
+  return 0
+end
+
+local function write(file, offset, value)
+  file:seek('set', offset)
+  file:write(string.char(value))
+  file:flush()
+end
+
+local MAX_ID = 2
+
+local function getId(self)
+  return self.initialized and 0 or 1
+end
+
+local function softUnlock(file, id)
+  write(file, MAX_ID + id, 0)
+end
+
+-- From Lamport's bakery algorithm
+local function softLock(file, id, try)
+  local max = 0
+  write(file, id, 1)
+  for j = MAX_ID, MAX_ID * 2 - 1 do
+    max = math.max(max, read(file, j))
+  end
+  local tic = 1 + max;
+  write(file, MAX_ID + id, tic)
+  write(file, id, 0)
+  --print(string.format("mutex_soft_init(%s, %s) max: %d", id, try, max));
+  if try and max ~= 0 then
+    softUnlock(file, id)
+    return false
+  end
+  for i = 0, MAX_ID - 1 do
+    if i ~= id then
+      while read(file, i) == 1 do
+        system.sleep(0)
+      end
+      local j = MAX_ID + i
+      while true do
+        local cur = read(file, j)
+        if cur ~= 0 and (cur < tic or (cur == tic and i < id)) then
+          system.sleep(0)
+        else
+          break
+        end
+      end
+    end
+  end
+  return true
+end
 
 return class.create(function(lock)
 
   function lock:initialize()
     self.name = string.format('.%s-%p.tmp', 'jls.lang.Lock', self)
     self.file = io.open(self.name, 'w+')
     self.initialized = true
+    self.file:write(string.rep('\0', MAX_ID * 2))
+    self.file:flush()
   end
 
   function lock:finalize()
@@ -17,33 +79,15 @@ return class.create(function(lock)
   end
 
   function lock:lock()
-    local b
-    repeat
-      self.file:seek('set')
-      b = self.file:read(1)
-      -- we may want to sleep in case of multiple failures
-    until b ~= 'l'
-    self.file:seek('set')
-    self.file:write('l')
-    self.file:flush()
+    softLock(self.file, getId(self), false)
   end
 
   function lock:unlock()
-    self.file:seek('set')
-    self.file:write(' ')
-    self.file:flush()
+    softUnlock(self.file, getId(self))
   end
 
   function lock:tryLock()
-    self.file:seek('set')
-    local b = self.file:read(1)
-    if b == 'l' then
-      return false
-    end
-    self.file:seek('set')
-    self.file:write('l')
-    self.file:flush()
-    return true
+    return softLock(self.file, getId(self), true)
   end
 
   function lock:toReference()

jls/lang/Lock-buffer.lua

@@ -1,9 +1,18 @@
+--- Provides mutual exclusion for the threads in the current process.
+-- @module jls.lang.Lock
+-- @pragma nostrip
+
 local class = require('jls.lang.class')
 
 local bufferLib = require('buffer')
+assert(type(bufferLib.initmutex) == 'function', 'bad buffer lib version '..tostring(bufferLib._VERSION))
 
+--- The Lock class.
+-- @type Lock
 return class.create(function(lock)
 
+  --- Creates a new Lock.
+  -- @function Lock:new
   function lock:initialize()
     self.mutex = bufferLib.newmutex()
     bufferLib.initmutex(self.mutex)
@@ -18,24 +27,33 @@ return class.create(function(lock)
     end
   end
 
+  --- Acquires the lock, blocking if necessary.
   function lock:lock()
     bufferLib.lock(self.mutex)
   end
 
+  --- Releases the lock.
   function lock:unlock()
     bufferLib.unlock(self.mutex)
   end
 
+  --- Returns true if the lock has been acquired without blocking.
+  -- @treturn boolean true if the lock has been acquired
   function lock:tryLock()
     return bufferLib.trylock(self.mutex)
   end
 
+  --- Returns a reference for this lock.
+  -- @treturn string a reference for this lock
   function lock:toReference()
     return bufferLib.toreference(self.mutex, nil, 'jls.lang.Lock')
   end
 
 end, function(Lock)
 
+  --- Returns a lock shared by the specified reference.
+  -- @tparam string reference the reference
+  -- @return The shared lock
   function Lock.fromReference(reference)
     local m = bufferLib.fromreference(reference, nil, 'jls.lang.Lock')
     if type(m) ~= 'userdata' then