CODEWITHSUNDEEP
goversion-control
Ari Seyhun
Ari Seyhun

Reputation: 12531

Modify Golang internal file?

I had the idea of adding a sync.WaitGroup Limit(max int) function to resrict the number of the WaitGroup counter.

So I opened the waitgroup.go file in go/src/sync and made the changes, saved the file and tried testing it in a main.go file on my desktop. When I ran the file, it says:

$ go run main.go
wg.Limit undefined (type sync.WaitGroup has no field or method Limit)

To fix this error message, I copied the folder from go/src/sync into the folder on my desktop containing my main.go file and changed the import from sync to ./sync.

After running go run main.go this time, I got the following output:

$ go run main.go
sync\mutex.go:14:2: use of internal package not allowed
sync\pool.go:8:2: use of internal package not allowed
sync\rwmutex.go:8:2: use of internal package not allowed
sync\waitgroup.go:8:2: use of internal package not allowed

To fix these messages, I copied go/src/internal into the folder on my desktop containing my main.go file and I modified all the files in ./sync that reference internal/.. to ./internal/..

I run it again and I get the following output:

$ go run main.go
# _/C_/.../sync
sync\mutex.go:20: missing function body for "throw"
sync\pool.go:66: missing function body for "fastrand"
sync\pool.go:249: missing function body for "runtime_registerPoolCleanup"
sync\pool.go:250: missing function body for "runtime_procPin"
sync\pool.go:251: missing function body for "runtime_procUnpin"
sync\runtime.go:14: missing function body for "runtime_Semacquire"
sync\runtime.go:17: missing function body for "runtime_SemacquireMutex"
sync\runtime.go:23: missing function body for "runtime_Semrelease"
sync\runtime.go:36: missing function body for "runtime_notifyListAdd"
sync\runtime.go:39: missing function body for "runtime_notifyListWait"
sync\runtime.go:39: too many errors

How can I implement my simple idea by modifying the source files of go/src without receiving these errors?

Upvotes: 0

Views: 1185

Answers (2)

AleGra
AleGra

Reputation: 136

I really wouldn't do this by changing the standard library, but instead wrap the WaitGroup to keep track of the counter like so:

type wg_limit struct {
    wg           sync.WaitGroup
    current, max int
}

func (wgl *wg_limit) Add(delta int) error {
    if wgl.current+delta > wgl.max {
    return fmt.Errorf("counter exceeded (current: %d, max: %d)", wgl.current, wgl.max)
    }
    wgl.current += delta
    wgl.wg.Add(delta)
    return nil
}

func (wgl *wg_limit) Done() {
    wgl.current -= 1
    wgl.wg.Done()
}

Then init wg_limit with a value for max and use the resulting variable just like a WaitGroup:

wgl := wg_limit{max: 3}
if err := wgl.Add(1); err != nil {
    // go something()
    // ...
    wgl.Done()
}

If the WaitGroup counter would be exceeded by the delta of Add(delta), an error is returned and the WaitGroup is unchanged.

Upvotes: 0

Ari Seyhun
Ari Seyhun

Reputation: 12531

In your installation of Go, navigate to the src folder and run the file called run.bat which will recompile all the packages removing the first error you described.

Upvotes: 0

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