Context timeout not working as expected in golang - go

Question

Helo All,
New to golang and was debugging timeout issues in a production environment. Before making a call to the server we add a timeout of 50ms to context and fire a server call. If the response is not received within 50 ms we expect the application to move on and not wait for the response.
But while debugging, I capture the duration between we fire a server call and the response received (or error out), to my surprise the value at the time is much higher than 50 ms.
Client syntax -
ctx, cancel := context.WithTimeout(ctx, e.opts.Timeout)
defer cancel()
fireServerCall(ctx)
..
..
def fireServerCall(ctx context:Context){
startTime:=time.Now()
//call to the server
res, err:=callToServer(ctx)
if err!=nil{
//capture failure latency
return ....
}
//capture success latency
return ....
}
Has anyone ever faced any similar issue? Is this expected behaviour? How did you handle such cases?
Am I doing something incorrectly? Suggestions are welcome :)
Edit:
I am passing context in my original code but forgot to mention it here, just added it. That mean, I am passing the same context on which my client is waiting for server to respond within 50 ms.

Answer 1

You should pass created context to fireServerCall and callToServer functions
callToServer should consider passed context and monitor ctx.Done() channel to stop its execution accordingly
Answering to comment by #Bishnu:
Don't think this is needed. Did a test and even without passing ctx to callToServer() it works. The behaviour is not as expected under high load. Can you kindly share some document/test what you have pointed here?
Context timeout just can't work without context passing and checking its Done() channel. Context is not some kind of magic — simplifying it is just a struct with done channel which is closed by calling cancel function or when timeout occurs. Monitoring this channel — is responsibility of the innermost function that accepts it.
Example:
package main
import (
"context"
"fmt"
"time"
)
func callToServer(ctx context.Context) {
now := time.Now()
select {
case <-ctx.Done(): // context cancelled via cancel or deadline
case <-time.After(1 * time.Second): // emulate external call
}
fmt.Printf("callToServer: %v\n", time.Since(now))
}
func callToServerContextAgnostic(ctx context.Context) {
now := time.Now()
select {
case <-time.After(2 * time.Second): // emulate external call
}
fmt.Printf("callToServerContextAgnostic: %v\n", time.Since(now))
}
func main() {
ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
defer cancel()
callToServer(ctx)
ctx2, cancel2 := context.WithTimeout(context.Background(), 100*time.Millisecond)
defer cancel2()
callToServerContextAgnostic(ctx2)
}
Results:
callToServer: 100ms
callToServerContextAgnostic: 2s
You can launch it on Go Playground: https://go.dev/play/p/tIxjHxUzYfh
Note that many of the clients (from standard or third party libraries) monitors Done channel by themselves.
For example standard HTTP client:
c := &http.Client{} // client for all requests
ctx, cancel := context.WithTimeout(context.Background(), time.Duration(time.Millisecond*100))
defer cancel()
req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://google.com", nil)
if err != nil {
log.Fatal(err)
}
resp, err := c.Do(req) // will monitor `Done` channel for you
Some docs and articles:
https://pkg.go.dev/context
https://www.digitalocean.com/community/tutorials/how-to-use-contexts-in-go