bazinga

src/import/ExtractThread.lua

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+-- ROM extraction, off the main thread.  The extractor's require closure needs
+-- only love.filesystem, love.image, love.math and love.system, none of which
+-- are main-thread-only, so it runs here instead of as a coroutine the frame
+-- loop resumed for 8ms out of every 16.7ms.
+--
+-- The caller clears the stale cache and writes the completion marker itself;
+-- this only fills the tree between those two steps, so the "marker appears
+-- last" order isReady() depends on stays on one thread.
+
+require("love.filesystem")
+require("love.image")
+require("love.math")
+require("love.system")
+require("love.timer")
+
+local version, prefix, romData, progressName, resultName = ...
+
+local progressChannel = love.thread.getChannel(progressName)
+local resultChannel = love.thread.getChannel(resultName)
+
+-- RomExtractor:tick fires per item, thousands of times per import; a channel
+-- push each would cost more than the work it reports.
+local PROGRESS_HZ = 20
+
+local ok, err = pcall(function()
+  local CacheFs = require("src.import.CacheFs")
+  CacheFs.prefix = prefix
+
+  local manifest = require("src.import.RomManifest").decode(version)
+  local RomExtractor = version == "gold"
+    and require("src.import.RomExtractorGen2")
+    or require("src.import.RomExtractor")
+
+  local lastPush, lastStage = 0, nil
+  local extractor = RomExtractor.new(romData, manifest,
+    function(progress, total, stage, current, stageTotal)
+      local now = love.timer.getTime()
+      -- Stage changes always go through, or the caption goes stale.
+      if stage ~= lastStage or now - lastPush >= 1 / PROGRESS_HZ then
+        lastPush, lastStage = now, stage
+        progressChannel:push({
+          progress = progress, total = total, stage = stage,
+          current = current, stageTotal = stageTotal,
+        })
+      end
+    end)
+  extractor:run()
+end)
+
+resultChannel:push({ ok = ok, error = ok and nil or tostring(err) })