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5 changed files with 1 additions and 118 deletions

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# go-concurrency
Aims to learn the knowledge about concurrency in Go
## Flow control with channels
1. We can imagine that channel is a pipe, `chan<-` means to send a value into the channel. `<-chan` means to receive a value from the channel.
2. `select ... case` can execute sending value into a channel
## Range and Close
1. A sender can close a channel to indicate that no more values will be sent.
2. Receivers can test whether a channel has been closed by assigning a second parameter to the receive expression. `v, ok := <-ch`, `ok` is `false` if there are no more values to receive and the channel is closed.
3. The loop for `i:= range c` receives values from the channel repeatedly until it is closed.
4. Only the sender should close a channel, never the receiver. Sending on a closed channel will cause a panic.
5. Channels aren't like files; you don't usually need to close them. Closing is only necessary when the receiver must be told there are no more values coming, such as to terminate a `range` loop.
## Select
1. The `select` statement lets a goroutine wait on multiple communication operations
2. A `select` blocks until one of its cases can run, then it executes that case. It chooses one at random if multiple are ready
## Default selection
1. The `default` case in a `select` is run if no other case is ready.
2. Use a `default` case to try a send or receive without blocking
```
select {
case i:= <-c:
// use i
default:
// receive when c is blocked
}
```
Aims to learn the knowledge about concurrency in Go

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package main
import (
"log"
"time"
)
func main() {
tick := time.Tick(100 * time.Millisecond)
boom := time.After(5000 * time.Millisecond)
for {
select {
case <-tick:
log.Println("tick.")
case <-boom:
log.Println("boom")
return
default:
log.Println(" .")
time.Sleep(50 * time.Millisecond)
}
}
}

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package main
import (
"log"
)
func fibonacci(n int, ch chan int) {
x, y := 0, 1
for i := 0; i < n; i++ {
ch <- x
x, y = y, x+y
}
close(ch)
}
func main() {
ch := make(chan int, 10)
go fibonacci(cap(ch), ch)
for i := range ch {
log.Println(i)
}
log.Println("Done")
}

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package main
import "log"
func fibonacci(ch, quit chan int) {
x, y := 0, 1
for {
select {
case ch <- x:
x, y = y, x+y
case <-quit:
log.Println("quit")
return
}
}
}
func main() {
ch := make(chan int, 10)
quit := make(chan int)
go func() {
for i := 0; i < cap(ch); i++ {
log.Println(<-ch)
}
quit <- 0
}()
fibonacci(ch, quit)
}