1+ package main
2+
3+ import (
4+ "fmt"
5+ )
6+
7+ func main () {
8+ // read NOTE ONE below
9+ c1 := incrementor ("1" )
10+ c2 := incrementor ("2" )
11+ // NOTE TWO
12+ // the flow of code continues here in main
13+ // incrementor is called
14+ // launches goroutines
15+ // returns channels which will eventually be closed
16+ // by the code that is running in the goroutines
17+ // launched by incrementor
18+ // program flow in main continues on down vertically here
19+
20+ // NOTE THREE
21+ // you're passing into "fanIn" two channels
22+ // fanIn HAS TO pull values off of those channels
23+ // otherwise: DEADLOCK
24+ // fanIn will need to launch goroutines to pull those values
25+ c := fanIn (c1 , c2 )
26+
27+ // NOTE SEVEN
28+ // we are held up here
29+ // pulling values off of c
30+ // until c is closed
31+ // and all values have been pulled from c
32+ // at which point ...
33+ for n := range c {
34+ fmt .Println (n )
35+ }
36+
37+ // NOTE EIGHT
38+ // our program is done
39+ // flow of code exits out of main
40+ // program ends
41+ }
42+
43+ func incrementor (s string ) <- chan string {
44+ c := make (chan string )
45+ go func () {
46+ for i := 0 ; i < 20 ; i ++ {
47+ // NOTE NINE
48+ // use Sprint here, or Sprintln, not Sprintf
49+ // this code is formatted for Sprintln
50+ // Sprintf would need this
51+ // c <- fmt.Sprintf("Process: %v, printing %v", s, i)
52+ c <- fmt .Sprint ("Process: " + s + " printing:" , i )
53+ }
54+ // NOTE ONE
55+ // incrementor
56+ // every time it's called
57+ // create a channel, put values on the channel
58+ // ******** important ********
59+ // have some other goroutine somewhere
60+ // pulling values off the channel
61+ // ***************************
62+ // close the channel
63+ // return that closed channel
64+ // these "incrementor" goroutines are off and running
65+ close (c )
66+ }()
67+ return c
68+ }
69+
70+ // FAN IN
71+ func fanIn (input1 , input2 <- chan string ) <- chan string {
72+ c := make (chan string )
73+ done := make (chan bool )
74+
75+ // NOTE FOUR
76+ // these goroutines will pull values off the "incrementor" channels
77+ // I'm defining the func to have a channel as a parameter and
78+ // I'm passing the channels in as an argument
79+ // as this is good practice to avoid different channels
80+ // accessing the same data and creating a race condition
81+ // not needed here, but good practice
82+ // and good to know about
83+
84+ go func (x <- chan string ) {
85+ for n := range x {
86+ c <- n
87+ }
88+ done <- true
89+ }(input1 )
90+
91+ go func (x <- chan string ) {
92+ for n := range x {
93+ c <- n
94+ }
95+ done <- true
96+ }(input2 )
97+
98+ // NOTE FIVE
99+ // this will signal when we're done writing values to c
100+ go func () {
101+ <- done
102+ <- done
103+ close (c )
104+ }()
105+
106+ // NOTE SIX
107+ // all of the above code
108+ // just flows straight through
109+ // goroutines are launched
110+ // and even though they're not done processing
111+ // program flow comes to here and this func returns
112+ // the channel c
113+ return c
114+ }
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