parallel processing - worse case scenario: launched two copies of a program which appends lines to a file -


i have python program performs simple operation on file:

with open(self.cache_filename_url, "a", encoding="utf8") f:     w = csv.writer(f, delimiter=',', quotechar='"', lineterminator='\n')     w.writerow([cache_url, rpd_products])

as can see opens file , appends csv line it. lot, in loop.

i accidentally ran 2 copies of program simultaneously, think have been appending file simultaneously. trying determine worst-case-scenario file corruption.

do think writes @ least atomic operations in case? example wouldn't problem me:

old line old line new line written instance 1 new line written instance 2 new line written 1

this would problem me:

old line old line [half of new line written instance 1] [half of new line instance 2] etc

to put way, possible 2 append operations "interfere" each other?

edit: using windows 7

opening same file multiple times in shared write mode can problematic. and, if don't open in shared mode, you'll 1 of them throwing exceptions cannot open file.

if shared mode: both instances have own internal pointer. in cases, write independently. get:

process opens file, sets pointer end (byte 1024) process b opens file, sets pointer end (byte 1024) process b writes @ byte 1024 , closes file process writes @ byte 1024 , closes file.

both processes have written file @ same location. you've lost record process b, , depending on how close works (if truncates), if lines writes different lengths, part of process b if line longer.

if in exclusive mode, 1 process fail open file, , whatever exception handling have kick in.

which mode in can system dependent, python doesn't seem provide mechanisms controlling share mode.


Comments

Post a Comment

Popular posts from this blog

php - Vagrant up error - Uncaught Reflection Exception: Class DOMDocument does not exist -

i've set bento/ubuntu-16.04 vagrant box using php 5.6, , getting following error quite few times when try , run shell script: "uncaught reflection exception: class domdocument not exist". i've tried adding following top of script (not together), each no success: "sudo apt-get install php5.6-xml", "sudo apt-get install php5-xml", "sudo apt-get install php-dom" i've tried resetting server "sudo service apache2 restart". does have suggestions?
Read more

vue.js - Create hooks for automated testing -

Image
qa guys complained can't automate frontend testing. because our html looks same outside. lazy hack did this <template> <div :role="$options.name"> ... </div> </template> <script> export default { name: 'vmcomponentname' } </script> which takes name script , applies html. in browser get: <div role="vmcomponentname"> ... </div> line :role="$options.name" goes in every component. is there dry er solutions? please share. additional details i'll explain in details looking for. imagine have vmusercreate form creates user. test case can create user . to automatically test without role, have use following selector: .wrapper > .wrapper > .wrapper > .submit-button the test extremely brittle (will break lot). if use roles can use [role="vmusercreateform"] .submit-button selector. many folds less brittle. so basically, i'm ...
Read more

Add new key value to json node in java -

i have json file : { "id":1, "name":"abc", "addressdetails": { "city":"newyork" } } i wanted add 1 more key-value ("pincode" : "414141") node 'addressdetails'. i tried using : objectmapper mapper = new objectmapper(); jsonnode root = mapper.readtree(new file("d://test.json")); objectnode node = mapper.createobjectnode(); node.with("addressdetails").put("pincode", "414141"); but it's not getting added, there way can ? you can try you should modify file path objectmapper mapper = new objectmapper(); objectnode nodes = mapper.readvalue(new file("d:\\test.txt"), objectnode.class); nodes.with("addressdetails").put("pincode", "414141"); mapper.writer().writevalue(new file("d:\\test.txt"), nodes);
Read more