concurrency

问题 I have a set of Futures created by submitting Callable s to an Executor . Pseudo code: for all tasks futures.add(executor.submit(new callable(task))) Now I'd like to get all futures waiting at most n seconds until all complete. I know I can call Future#get(timeout) but if I call that sequentially for all my futures in a loop the timouts start adding up. Pseudo code: for all futures future.get(timeout) get blocks with a timeout until the result is ready. Therefore, if the first completes just

问题 func (this *l) PostUpload(ctx *Context) { //ctx.Response.Status = 500 l, err := models.NewL(this.Config) go func() { err = l.Save(file) if err != nil { ctx.Response.Status = 500 ctx.Response.Body = err } else { ctx.Response.Status = 204 } }() } How to change ctx.Response.Status value inside the goroutine closure? 回答1: You have no guarantee to observe changes made to the value of a variable in another goroutine without synchronization . See The Go Memory Model for details. So if you want to

问题 func (this *l) PostUpload(ctx *Context) { //ctx.Response.Status = 500 l, err := models.NewL(this.Config) go func() { err = l.Save(file) if err != nil { ctx.Response.Status = 500 ctx.Response.Body = err } else { ctx.Response.Status = 204 } }() } How to change ctx.Response.Status value inside the goroutine closure? 回答1: You have no guarantee to observe changes made to the value of a variable in another goroutine without synchronization . See The Go Memory Model for details. So if you want to

问题 I have several workers, each holding its own connection to PostgreSQL. The workers manipulate with different tables. The workers handle parallel requests from outside the system. One of the tables being accessed is the table of users. When some information comes, I first need to ensure there is a record for the user in the table. If there is no record, I wish to create one at first. I'm using the following idiom: if [user does not exist] then [create user] The code of [user does not exist] is

问题 I have several workers, each holding its own connection to PostgreSQL. The workers manipulate with different tables. The workers handle parallel requests from outside the system. One of the tables being accessed is the table of users. When some information comes, I first need to ensure there is a record for the user in the table. If there is no record, I wish to create one at first. I'm using the following idiom: if [user does not exist] then [create user] The code of [user does not exist] is

问题 In this article: http://www.drdobbs.com/parallel/volatile-vs-volatile/212701484?pgno=2 says, that we can't do any optimization for volatile , even such as (where: volatile int& v = *(address); ): v = 1; // C: write to v local = v; // D: read from v can't be optimized to this: v = 1; // C: write to v local = 1; // D: read from v // but it can be done for std::atomic<> It is can't be done, because between 1st and 2nd lines may v value be changed by hardware device (not CPU where can't work

问题 I have a script where I parallelize job execution while monitoring the progress. I do this using xargs and a named fifo pipe. My problem is that I while xargs performs well, some lines written to the pipe are lost. Any idea what the problem is? For example the following script (basically my script with dummy data) will produce the following output and hangs at the end waiting for those missing lines: $ bash test2.sh Progress: 0 of 99 DEBUG: Processed data 0 in separate process Progress: 1 of

问题 I have the following code: package main import ( "fmt" "time" ) type Response struct { Data string Status int } func main() { var rc [10]chan Response for i := 0; i < 10; i++ { rc[i] = make(chan Response) } var responses []Response for i := 0; i < 10; i++ { go func(c chan<- Response, n int) { c <- GetData(n) close(c) }(rc[i], i) } for _, resp := range rc { responses = append(responses, <-resp) } for _, item := range responses { fmt.Printf("%+v\n", item) } } func GetData(n int) Response { time

问题 It seems to me that file writing in Ruby MRI 1.8.7 is completely thread safe. Example 1 - Flawless Results: File.open("test.txt", "a") { |f| threads = [] 1_000_000.times do |n| threads << Thread.new do f << "#{n}content\n" end end threads.each { |t| t.join } } Example 2 - Flawless Results (but slower): threads = [] 100_000.times do |n| threads << Thread.new do File.open("test2.txt", "a") { |f| f << "#{n}content\n" } end end threads.each { |t| t.join } So, I couldn't reconstruct a scenario

问题 It seems to me that file writing in Ruby MRI 1.8.7 is completely thread safe. Example 1 - Flawless Results: File.open("test.txt", "a") { |f| threads = [] 1_000_000.times do |n| threads << Thread.new do f << "#{n}content\n" end end threads.each { |t| t.join } } Example 2 - Flawless Results (but slower): threads = [] 100_000.times do |n| threads << Thread.new do File.open("test2.txt", "a") { |f| f << "#{n}content\n" } end end threads.each { |t| t.join } So, I couldn't reconstruct a scenario