Ruby DB-connection (SQLITE) with concurrent gem - ruby

Question

I have a question and already the workaround for it, but I am not sure if this is "right" solution.
The followning example does not work. It gets stuck by the SQL-Update.
def mysynccmd(username,log)
exit_code = system("Doing stuff")
if exit_code != true
log.error "Error: #{username} not done."
else
log.info "Successfully done user: #{username}"
end
return exit_code
end
# Create thread pool
pool = Concurrent::FixedThreadPool.new(threadlimit)
# Running loop over the list of users with status 0
begin
#SQLite3::Database.new(dbfile) do |db|
db = SQLite3::Database.open dbfile
db.execute( "SELECT user FROM T_users WHERE status = 0" ) do |user|
# Puts work into the thread pool
pool.post do
# Check if the sync was correct and update the DB
if mysynccmd(user[0],log) == true
db.execute("UPDATE T_users SET status=1 WHERE user = '#{username}';")
end
end
end
#end
rescue SQLite3::Exception => e
log.error "Exception occurred: #{e}"
ensure
db.close if db
end
And I was thinking during the multithreading the DB-connection gets lost, because of the new process/thread.
So I did it this way and opend a new connection in every thread.
def mysynccmd(username,log,dbfile)
exit_code = system("Doing stuf")
if exit_code != true
log.error "Error: #{username} is not done."
else
log.info "Successfully done user: #{username}"
begin
db = SQLite3::Database.open dbfile
db.execute("UPDATE T_users SET status=1 WHERE user = '#{username}';")
rescue SQLite3::Exception => e
log.error "mysynccmd: Exception occurred: #{e}"
ensure
db.close if db
end
end
end
# Create thread pool
pool = Concurrent::FixedThreadPool.new(threadlimit)
# Running loop over the list of not synced users
begin
#SQLite3::Database.new(dbfile) do |db|
db = SQLite3::Database.open dbfile
db.execute( "SELECT user FROM T_users WHERE status = 0" ) do |user|
# Puts work into the thread pool
pool.post do
# Check if the sync was correct and update the DB
mysynccmd(user[0],log,dbfile)
end
end
#end
rescue SQLite3::Exception => e
log.error "Exception occurred: #{e}"
ensure
db.close if db
end
Was my thinking right or wrong?
Thanks for your answers and/or alternative ideas.