feat(exit): add exit signalling (#172)

Author: Tieske

docs/index.html

@@ -104,6 +104,8 @@ <h2><a name="history"></a>History</h2>
         <li>Change: Copas no longer requires LuaSocket, if no sockets are needed, LuaSystem will be enough as a fallback.</li>
         <li>Feat: added <code>copas.gettime()</code>, which transparently maps to either LuaSockets or
         LuaSystems implementation, ensuring independence of the availability of either one of those.</li>
+        <li>Feat: Controlled exit of the Copas loop. Adding <code>copas.exit()</code>, <code>copas.exiting()</code>, and
+        <code>copas.waitforexit()</code>.</li>
     </ul></dd>
 
     <dt><strong>Copas 4.7.1</strong> [9/Mar/2024]</dt>

docs/reference.html

@@ -81,8 +81,12 @@ <h3>Getting started examples</h3>
 
 end
 
-copas.addserver(server_socket, copas.handler(connection_handler,
-    ssl_params), "my_TCP_server")
+copas.addthread(function()
+    copas.addserver(server_socket, copas.handler(connection_handler,
+        ssl_params), "my_TCP_server")
+    copas.waitforexit()
+    copas.removeserver(server_socket)
+end)
 
 copas()
 </pre>
@@ -180,6 +184,29 @@ <h3>Copas dispatcher main functions</h3>
         truthy.</p>
     </dd>
 
+    <dt><strong><code>copas.exit()</code></strong></dt>
+    <dd>
+        <p>Sets a flag that the application is intending to exit. After calling
+        this function <code>copas.exiting()</code> will be returning <code>true</code>, and
+        all threads blocked on <code>copas.waitforexit()</code> will be released.</p>
+
+        <p>Copas itself will call this function when <code>copas.finished()</code> returns
+        <code>true</code>.</p>
+    </dd>
+
+    <dt><strong><code>bool = copas.exiting()</code></strong></dt>
+    <dd>
+        <p>Returns a flag indicating whether the application is supposed to exit.
+        Returns <code>false</code> until after <code>copas.exit()</code> has been called,
+        after which it will start returning <code>true</code>.</p>
+
+        <p>Clients should check whether they are to cease their operation and exit. They
+        can do this by checking this flag, or by registering a task waiting on
+        <code>copas.waitforexit()</code>. Clients should cancel pending work and close sockets
+        when an exit is announced, otherwise Copas will not exit.
+        </p>
+    </dd>
+
     <dt><strong><code>bool = copas.finished()</code></strong></dt>
     <dd>
         <p>Checks whether anything remains to be done.</p>
@@ -304,6 +331,15 @@ <h3>Copas dispatcher main functions</h3>
         currently running coroutine.</p>
     </dd>
 
+    <dt><strong><code>copas.waitforexit()</code></strong></dt>
+    <dd>
+        <p>This will block the calling coroutine until the <code>copas.exit()</code> function
+        is called. Clients should check whether they are to cease their operation and exit. They
+        can do this by waiting on this call, or by checking the <code>copas.exiting()</code> flag.
+        Clients should cancel pending work and close sockets when an exit is announced, otherwise
+        Copas will not exit.</p>
+    </dd>
+
     <dt><strong><code>skt = copas.wrap(skt [, sslparams] )</code></strong></dt>
     <dd>
         <p>Wraps a LuaSocket socket and returns a Copas socket that implements LuaSocket's API

src/copas.lua

@@ -1666,6 +1666,38 @@ function copas.finished()
   return #_reading == 0 and #_writing == 0 and _resumable:done() and _sleeping:done(copas.gettimeouts())
 end
 
+
+local resetexit do
+  local exit_semaphore, exiting
+
+  function resetexit()
+    exit_semaphore = copas.semaphore.new(1, 0, math.huge)
+    exiting = false
+  end
+
+  -- Signals tasks to exit. But only if they check for it. By calling `copas.exiting`
+  -- they can check if they should exit. Or by calling `copas.waitforexit` they can
+  -- wait until the exit signal is given.
+  function copas.exit()
+    if exiting then return end
+    exiting = true
+    exit_semaphore:destroy()
+  end
+
+  -- returns whether Copas is in the process of exiting. Exit can be started by
+  -- calling `copas.exit()`.
+  function copas.exiting()
+    return exiting
+  end
+
+  -- Pauses the current coroutine until Copas is exiting. To be used as an exit
+  -- signal for tasks that need to clean up before exiting.
+  function copas.waitforexit()
+    exit_semaphore:take(1)
+  end
+end
+
+
 local _getstats do
   local _getstats_instrumented, _getstats_plain
 
@@ -1756,8 +1788,17 @@ function copas.loop(initializer, timeout)
     timeout = initializer or timeout
   end
 
+  resetexit()
   copas.running = true
-  while not copas.finished() do copas.step(timeout) end
+  while true do
+    copas.step(timeout)
+    if copas.finished() then
+      if copas.exiting() then
+        break
+      end
+      copas.exit()
+    end
+  end
   copas.running = false
 end
 

tests/exittest.lua

@@ -72,3 +72,46 @@ copas.loop()
 assert(testran == 6, "Test 6 was not executed!")
 print("6) success")
 
+print("7) Testing exiting releasing the exitsemaphore (implicit, no call to copas.exit)")
+copas.addthread(function()
+  print("","7 running...")
+  copas.addthread(function()
+    copas.waitforexit()
+    testran = 7
+  end)
+end)
+copas.loop()
+assert(testran == 7, "Test 7 was not executed!")
+print("7) success")
+
+print("8) Testing schduling new tasks while exiting (explicit exit by calling copas.exit)")
+testran = 0
+copas.addthread(function()
+  print("","8 running...")
+  copas.addthread(function()
+    while true do
+      copas.pause(0.1)
+      testran = testran + 1
+      print("count...")
+      if testran == 3 then  -- testran == 3
+        print("initiating exit...")
+        copas.exit()
+        break
+      end
+    end
+  end)
+  copas.addthread(function()
+    copas.waitforexit()
+    print("exit signal received...")
+    testran = testran + 1   -- testran == 4
+    copas.addthread(function()
+      print("running new task from exit handler...")
+      copas.pause(1)
+      testran = testran + 1 -- testran == 5
+      print("new task from exit handler done!")
+    end)
+  end)
+end)
+copas.loop()
+assert(testran == 5, "Test 8 was not executed!")
+print("8) success")