coverbrowser: keep up to date with recent core changes (#3707)

Remove the subprocess management functions from xutil.lua, as they were
moved into base/ffi/util.lua, and use them from there.
Also use the cre_storage_size_factor setting when processing credocuments,
to avoid CRE WARNING while indexing too.
Fix dealing with MuPDF document opening failures (previously, these
were not noticed and indexing was retried each time).

plugins/coverbrowser.koplugin/bookinfomanager.lua

@@ -308,7 +308,8 @@ function BookInfoManager:extractBookInfo(filepath, cover_specs)
         -- cre.initCache("", 1024*1024*32) -- empty path = no cache
         -- But it's best to use a cache for quicker and less memory
         -- usage when opening big books:
-        cre.initCache(self.tmpcr3cache, 0) -- 0 = previous book caches are removed when opening a book
+        cre.initCache(self.tmpcr3cache, 0, -- 0 = previous book caches are removed when opening a book
+            true, G_reader_settings:readSetting("cre_storage_size_factor")) -- avoid CRE WARNINGs
         self.cre_cache_overriden = true
     end
 
@@ -440,6 +441,8 @@ function BookInfoManager:extractBookInfo(filepath, cover_specs)
             end
         end
         DocumentRegistry:closeDocument(filepath)
+    else
+        loaded = false
     end
     if not loaded then
         dbrow.unsupported = _("not readable by engine")
@@ -513,7 +516,7 @@ function BookInfoManager:collectSubprocesses()
         local i = 1
         while i <= #self.subprocesses_pids do -- clean in-place
             local pid = self.subprocesses_pids[i]
-            if xutil.isSubProcessDone(pid) then
+            if util.isSubProcessDone(pid) then
                 table.remove(self.subprocesses_pids, i)
             else
                 i = i + 1
@@ -551,7 +554,7 @@ end
 function BookInfoManager:terminateBackgroundJobs()
     logger.dbg("terminating", #self.subprocesses_pids, "subprocesses")
     for i=1, #self.subprocesses_pids do
-        xutil.terminateSubProcess(self.subprocesses_pids[i])
+        util.terminateSubProcess(self.subprocesses_pids[i])
     end
 end
 
@@ -587,7 +590,7 @@ function BookInfoManager:extractInBackground(files)
     self.cleanup_needed = true -- so we will remove temporary cache directory created by subprocess
 
     -- Run task in sub-process, and remember its pid
-    local task_pid = xutil.runInSubProcess(task)
+    local task_pid = util.runInSubProcess(task)
     if not task_pid then
         logger.warn("Failed lauching background extraction sub-process (fork failed)")
         return false -- let caller know it failed

plugins/coverbrowser.koplugin/xutil.lua

@@ -1,56 +1,9 @@
 local ffi = require("ffi")
-local C = ffi.C
 
 -- Utilities functions needed by this plugin, but that may be added to
 -- existing base/ffi/ files
 local xutil = {}
 
-
--- Sub-process management (may be put into base/ffi/util.lua)
-function xutil.runInSubProcess(func)
-    local pid = C.fork()
-    if pid == 0 then -- child process
-        -- Just run the provided lua code object in this new process,
-        -- and exit immediatly (so we do not release drivers and
-        -- resources still used by parent process)
-        func()
-        os.exit(0)
-    end
-    -- parent/main process, return pid of child
-    if pid == -1 then -- On failure, -1 is returned in the parent
-        return false
-    end
-    return pid
-end
-
-function xutil.isSubProcessDone(pid)
-    local status = ffi.new('int[1]')
-    local ret = C.waitpid(pid, status, 1) -- 1 = WNOHANG : don't wait, just tell
-    -- status = tonumber(status[0])
-    -- local logger = require("logger")
-    -- logger.dbg("waitpid for", pid, ":", ret, "/", status)
-    -- still running: ret = 0 , status = 0
-    -- exited: ret = pid , status = 0 or 9 if killed
-    -- no more running: ret = -1 , status = 0
-    if ret == pid or ret == -1 then
-        return true
-    end
-end
-
-function xutil.terminateSubProcess(pid)
-    local done = xutil.isSubProcessDone(pid)
-    if not done then
-        -- local logger = require("logger")
-        -- logger.dbg("killing subprocess", pid)
-        -- we kill with signal 9/SIGKILL, which may be violent, but ensures
-        -- that it is terminated (a process may catch or ignore SIGTERM)
-        C.kill(pid, 9)
-        -- process will still have to be collected with calls to util.isSubProcessDone(),
-        -- which may still return false for some small amount of time after our kill()
-    end
-end
-
-
 -- Data compression/decompression of strings thru zlib (may be put in a new base/ffi/zlib.lua)
 -- from http://luajit.org/ext_ffi_tutorial.html
 ffi.cdef[[
@@ -79,7 +32,6 @@ function xutil.zlib_uncompress(zdata, datalen)
     return ffi.string(buf, buflen[0])
 end
 
-
 -- Not provided by base/thirdparty/lua-ljsqlite3/init.lua
 -- Add a timeout to a lua-ljsqlite3 connection
 -- We need that if we have multiple processes accessing the same