improved interruption (SIGINT, CTRL+C) support

* Just like the original LuaJIT interpreter, this will use a hook to automatically
  raise an error from Lua code.
* Unfortunately, as long as Jit compilation is enabled, this cannot reliably work.
  Therefore we still set an `interrupted` flag that must be
  polled from tight loops.
* Instead of polling via applause_push_sample() which gave interruption-support only
  to Stream:play(), we now have a separate checkint() function.
* checkint() should be manually added to all tight loops.
* Stream:foreach() and everthing based on it is now also supporting interruptions
  (via checkint()).
* This internally works via applause_is_interrupted().
  A C function was exposed only because LuaJIT does not support volatile-qualifiers and
  would optimize away reads to the interrupted-flag.
  As a side effect, we can also reset the hook.
* Flags set in signal handlers should be `volatile`.
* Added likely() and unlikely() macros to C code.
* Updated sample.ipynb Jupyter notebook: Everything important is now supported, albeit
  requiring custom ILua patches.

1 files changed, 27 insertions, 21 deletions

diff --git a/applause.lua b/applause.lua
index 702e1ce..702913d 100644
--- a/applause.lua
+++ b/applause.lua
@@ -32,6 +32,22 @@ end
 
 cdef_include "applause.h"
 
+--- Check whether the process was interrupted (SIGINT received).
+--
+-- This checks and automatically raises an error if CTRL+C was pressed
+-- or SIGINT was received.
+-- The automatic way to handle SIGINT is **not** reliable in LuaJIT.
+-- A call to this function should therefore be added to all tight
+-- loops.
+function checkint()
+	-- This does not poll the interrupted-flag directly
+	-- since LuaJIT does not support volatile qualifiers and could
+	-- optimize the read away.
+	if C.applause_is_interrupted() ~= 0 then
+		error("SIGINT received", 2)
+	end
+end
+
 --
 -- Define C functions for benchmarking (POSIX libc)
 --
@@ -664,8 +680,7 @@ function Stream:play(first_port)
 	local old_stepmul = collectgarbage("setstepmul", 100)
 
 	local channels = self.channels
-	local state
-	self:foreach(function(frame)
+	local _, err = pcall(Stream.foreach, self, function(frame)
 		-- Loop should get unrolled automatically
 		for i = 1, channels do
 			local sample = tonumber(frame[i])
@@ -674,7 +689,7 @@ function Stream:play(first_port)
 			-- NOTE: Invalid port Ids are currently silently
 			-- ignored. Perhaps it's better to check state or
 			-- to access output_ports_count from applause.c.
-			state = C.applause_push_sample(first_port+i, sample)
+			local state = C.applause_push_sample(first_port+i, sample)
 
 			-- React to buffer underruns.
 			-- This is done here instead of in the realtime thread
@@ -683,17 +698,13 @@ function Stream:play(first_port)
 			if state == C.APPLAUSE_AUDIO_XRUN then
 				io.stderr:write("WARNING: Buffer underrun detected\n")
 			end
-
-			if state == C.APPLAUSE_AUDIO_INTERRUPTED then return true end
 		end
 	end)
 
 	collectgarbage("setpause", old_pause)
 	collectgarbage("setstepmul", old_stepmul)
 
-	if state == C.APPLAUSE_AUDIO_INTERRUPTED then
-		error("SIGINT received", 2)
-	end
+	if err then error(err, 2) end
 end
 
 --- Execute function for each frame generated by the stream.
@@ -702,21 +713,19 @@ end
 -- @func fnc
 --   Function to execute.
 --   It gets passed an array of samples, one for each channel.
--- @fixme This is not currently interruptable and therefore not suitable
--- to be executed dynamically at the command-line.
+--   If it returns true, the loop is terminated.
 function Stream:foreach(fnc)
-	local clear = table.clear
-
 	-- NOTE: This implementation is for single-channel streams
 	-- only. See also MuxStream:foreach().
+	local clear = table.clear
 	local frame = table.new(1, 0)
 	local tick = self:gtick()
 
-	while true do
+	repeat
+		checkint()
 		frame[1] = tick()
 		clear(sampleCache)
-		if not frame[1] or fnc(frame) then break end
-	end
+	until not frame[1] or fnc(frame)
 end
 
 --- Benchmark stream (time to generate all samples).
@@ -873,8 +882,6 @@ end
 -- @string[opt="full"] vbufmode Buffering mode.
 -- @int[opt] vbufsize The buffer size.
 -- @see file:setvbuf
--- @fixme This is currently allowed for infinite streams as well,
--- but there is no way to interrupt Stream:foreach().
 function Stream:pipe(prog, vbufmode, vbufsize)
 	local hnd = io.popen(prog, "w")
 	hnd:setvbuf(vbufmode or "full", vbufsize)
@@ -1282,7 +1289,8 @@ function MuxStream:foreach(fnc)
 	local channels = self.channels
 	local frame = table.new(channels, 0)
 
-	while true do
+	repeat
+		checkint()
 		clear(sampleCache)
 
 		for i = 1, channels do
@@ -1291,9 +1299,7 @@ function MuxStream:foreach(fnc)
 			-- length, if one ends all end
 			if not frame[i] then return end
 		end
-
-		if fnc(frame) then break end
-	end
+	until fnc(frame)
 end
 
 --- Mux several streams with the source stream into a multi-channel stream.