Dear Community and dear Go-developers, Meanwhile it is clear why things do not work: The Go-Scheduler is unable to allow to switch to another goroutine in busy-waiting-loops - the only possibility to get around that problem is either to put "switch-steps" into the source - either "time.Sleep(1)" or "runtime.Gosched()". I think that THIS SHOULD BE DOCUMENTED IN THE LANGUAGE SPECIFICATION !!!!!
(See my book on https://maurer-berlin.eu/nspbuch - in it's 4th edition things are mentioned.) With kind regards, Christian Maurer Am Montag, 30. Oktober 2017 18:30:06 UTC+1 schrieb Christian Maurer: > > Dear Go-community, > > I noticed a very strange effect by translating the > mutual exclusion algorithm of E. W. Dijkstra to Go. > Reference: > Cooperating Sequential Processes. Technical Report EWD-123, > Technological University Eindhoven (1965) > http://www.cs.utexas.edu/users/EWD/ewd01xx/EWD123.PDF) > > Inserting or omitting code lines A and B resp. > changes the behaviour of this program very severely: > > With line A and without line B: > mutual exclusion is not guaranteed, > with line B and without line A: > lock does not terminate and > with both lines: > the program works as it should. > > --- 8< -------------------------------------------- > package main > > import ( > "math/rand" > "time" > ) > > const N = 10 // number of goroutines involved > > var ( > turn int > b, c = make([]int, N+1), make([]int, N+1) > n = uint(0) > inCS = make([]bool, N+1) > s = make([]string, N+1) > done = make(chan int) > ) > > func chk(i int) { > for j := 1; j <= N; j++ { > if j != i && inCS[j] { > panic("oops") > } > } > } > > func lock(i int) { > b[i] = 0 > L: > if turn != i { > c[i] = 1 > if b[turn] == 1 { > turn = i > goto L > } > } > time.Sleep(1) // A > c[i] = 0 > time.Sleep(1) // B > for j := 1; j <= N; j++ { > if j != i && c[j] == 0 { > goto L > } > } > inCS[i] = true > chk(i) > } > > func unlock(i int) { > inCS[i] = false > c[i], b[i] = 1, 1 > // turn = 0 // does not matter > } > > func v() { > time.Sleep(time.Duration(1e7 + rand.Int63n(1e7))) > } > > func count(i int) { > for k := 0; k < 100; k++ { > lock(i) > accu := n > v() > accu++ > v() > n = accu > v() > println(s[i], n) > unlock(i) > v() > } > done <- 0 > } > > func main() { > s[1] = "" > for i := 2; i <= N; i++ { > s[i] = s[i-1] + " " > } > for i := 1; i <= N; i++ { > go count(i) > } > for i := 1; i <= N; i++ { > <-done > } > } > --- >8 -------------------------------------------- > > The cause for the "freaking out" of the program without > those compulsory breaks (of only 1 ns) is absolutely unclear. > > Any sort of help is welcome! > > Kind regards to everybody, > > Christian Maurer > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/f83856a2-0661-4425-9861-196b83fcf07f%40googlegroups.com.
