concurrency

问题 I am writing a simple synchronous download manager which downloads a video file in 10 sections. I am using requests to get content-length from headers. Using this I am breaking and downloading files in 10; byte chunks and then merging them to form a complete video. The code below suppose to work this way but the end merged file only works for seconds and after that it gets corrupted. What is wrong in my code? import requests import os def intervals(parts, duration): part_duration = duration /

问题 I have an API that in order to insert a new item it needs to be validated. The validation basically is a type validator( string , number , Date , e.t.c) and queries the database that checks if the "user" has an "item" in the same date, which if it does the validation is unsuccessful. Pseudocode goes like this: const Item = require("./models/item"); function post(newDoc){ let errors = await checkForDocErrors(newDoc) if (errors) { throw errors; } let itemCreated = await Item.create(newDoc);

问题 I have an API that in order to insert a new item it needs to be validated. The validation basically is a type validator( string , number , Date , e.t.c) and queries the database that checks if the "user" has an "item" in the same date, which if it does the validation is unsuccessful. Pseudocode goes like this: const Item = require("./models/item"); function post(newDoc){ let errors = await checkForDocErrors(newDoc) if (errors) { throw errors; } let itemCreated = await Item.create(newDoc);

问题 I have an API that in order to insert a new item it needs to be validated. The validation basically is a type validator( string , number , Date , e.t.c) and queries the database that checks if the "user" has an "item" in the same date, which if it does the validation is unsuccessful. Pseudocode goes like this: const Item = require("./models/item"); function post(newDoc){ let errors = await checkForDocErrors(newDoc) if (errors) { throw errors; } let itemCreated = await Item.create(newDoc);

问题 I have an API that in order to insert a new item it needs to be validated. The validation basically is a type validator( string , number , Date , e.t.c) and queries the database that checks if the "user" has an "item" in the same date, which if it does the validation is unsuccessful. Pseudocode goes like this: const Item = require("./models/item"); function post(newDoc){ let errors = await checkForDocErrors(newDoc) if (errors) { throw errors; } let itemCreated = await Item.create(newDoc);

问题 I use a query like this: INSERT INTO table SELECT * FROM table2 t2 JOIN ... ... WHERE table2.date < now() - '1 day'::INTERVAL FOR UPDATE OF t2 SKIP LOCKED ON CONFLICT (...) DO UPDATE SET ... RETURNING *; My question is about FOR UPDATE t2 SKIP LOCKED . Should I use it here? Or will Postgres lock these rows automatically with INSERT SELECT ON CONFLICT till the end of the transaction? My goal is to prevent other apps from (concurrently) capturing rows with the inner SELECT which are already

问题 I have the following code:- extension Collection { // EZSE : A parralelized map for collections, operation is non blocking public func pmap<R>(_ each: (Self.Iterator.Element) -> R) -> [R?] { let indices = indicesArray() var res = [R?](repeating: nil, count: indices.count) DispatchQueue.concurrentPerform(iterations: indices.count) { (index) in let elementIndex = indices[index] res[index] = each(self[elementIndex]) } // Above code is non blocking so partial exec on most runs return res } ///

问题 I have the following code:- extension Collection { // EZSE : A parralelized map for collections, operation is non blocking public func pmap<R>(_ each: (Self.Iterator.Element) -> R) -> [R?] { let indices = indicesArray() var res = [R?](repeating: nil, count: indices.count) DispatchQueue.concurrentPerform(iterations: indices.count) { (index) in let elementIndex = indices[index] res[index] = each(self[elementIndex]) } // Above code is non blocking so partial exec on most runs return res } ///

问题 I want to write a simple thread-safe arraylist which supports: add(), remove(int i), insert(int i), update(int i), and get(int i) One simple implementation is to add lock to the internal data structure(an object array for example), but it is not good enough because only one thread could access the list at a time. Therefore my initial plan is to add lock to each data slot so that different threads could have access to elements in different indexes at the same time. The data structure will look

问题 I want to write a simple thread-safe arraylist which supports: add(), remove(int i), insert(int i), update(int i), and get(int i) One simple implementation is to add lock to the internal data structure(an object array for example), but it is not good enough because only one thread could access the list at a time. Therefore my initial plan is to add lock to each data slot so that different threads could have access to elements in different indexes at the same time. The data structure will look