how to implement coroutine lock in tornado

Question

i understand the mechanism of corountine in Tornado ,but here is the problem i couldn't figure out,please give me a hand

consider this business routine : here are 5 database operations

#operation 1
#use asynchronous method ,doesn't matter
#switch to other coroutine

#operation 2
#use asynchronous method ,doesn't matter
#switch to other coroutine


#operation 3
#use asynchronous method , but i'll use the result do 
#some process then update in operation 4
#switch to other coroutine


#operation 4
#use asynchronous method ,doesn't matter
#switch to other coroutine


#operation 5
#use asynchronous method ,doesn't matter
#switch to other coroutine

as you can see, i don't hope any other related coroutine do update to the same table or same record between each one's operation 3 and operation 4,it'll make dirty read and write.in other words

#coroutine 1 operation 3
#coroutine 2 operation 3
#coroutine 1 operation 4
#coroutine 2 operation 4

would not be accepted, the proper order should be

#coroutine 1 operation 3
#coroutine 1 operation 4
#coroutine 2 operation 3
#coroutine 2 operation 4

i can use block method at operation 3 ,but that'll block the whole server,i hope the main loop would Not execute certain coroutines until i told them to release.

Answer 1

this was silly after i think it over.

this was really really simple and basic in a single thread program practice

global flag
while flag:
    do some asynchronous empty callback
flag = True

#operation 3
#use asynchronous method , but i'll use the result do 
#some process then update in operation 4
#switch to other coroutine

#operation 4
#use asynchronous method ,doesn't matter
#switch to other coroutine

flag = False

Done.