Adding support for context.Context

[xiam]

Hey @pkieltyka,

This work in progress features code changes for chainstore and a new mockstore store that I'm using to test the chainstore with context.Context. The intention of this PR is to review the code changes in chainstore and see if we can start updating the other stores to reflect changes in the interface.

See: #8

[xiam]

We could add a "opened" property here, if required.

[xiam]

Hey @VojtechVitek,

I had to modify your snippet a bit, what do you think of the new location of the range over putBack? Otherwise it just stays blocked waiting for a value to arrive.

[VojtechVitek]

Did it block because the channel was unbuffered?
putBack := make(chan Store, len(c.stores)) shouldn't block, I can't imagine how.

[VojtechVitek]

Taking that back ... obviously not, let me see the code again :) I was throwing it of top of my head. But this looks good already :)

[VojtechVitek]

Hey, I have a working snippet for you... without firstVal channel and the extra goroutine:

package main

import (
    "errors"
    "fmt"
    "time"

    "golang.org/x/net/context"
)

func Get(ctx context.Context) (string, error) {
    nextStore := make(chan string, 3)
    for _, store := range []string{"first", "second", "third"} {
        nextStore <- store
    }
    close(nextStore)

    putBack := make(chan string, 3)

    for {
        select {
        case <-ctx.Done():
            return "", ctx.Err()
        case store, ok := <-nextStore:
            if !ok {
                return "", errors.New("not found")
            }

            if store != "fourth" { // change this --- simulating what store returns FOUND
                putBack <- store
                break
            }
            close(putBack)

            for store := range putBack {
                go fmt.Printf("putting back to %v store\n", store)
            }

            return fmt.Sprintf("found in %v", store), nil
        }
    }

    panic("unreachable")
}

func main() {
    ctx, _ := context.WithTimeout(context.Background(), time.Second)
    val, err := Get(ctx)
    fmt.Println(val, err)

    // wait for fmt.Printf() from goroutines
    time.Sleep(time.Second)
}

[xiam]

Cool! makes sense, the close(putBack) is what makes the range not to lock. I like it.

[xiam]

I tried closing the channel and everything worked fine :).

[xiam]

All right, I also updated all the other stores, their tests and the example. Now everything is working as before.

[VojtechVitek]

LGTM :)

@xiam can you add document changing the .Get() and .Put() API in the project README and reference the last commit/tag of the old API?