Errors

Sentinel errors

Error	Returned by	Meaning
ErrPoolClosed	every submit, and waiters on dropped jobs	the pool is closed or closing
ErrPoolFull	TrySubmit, TrySubmitJob, RateLimiter.TrySubmit	the queue is full
ErrInvalidConfig	NewPool	an option is out of range; wrapped with details
ErrJobPanic	jobs that panicked	matched by every *PanicError
ErrRateLimited	RateLimiter.TrySubmit	no token is available
ErrLimiterStopped	RateLimiter.Submit, RateLimiter.TrySubmit	the rate limiter was stopped

Match them with errors.Is:

switch err := pool.TrySubmit(job); {
case err == nil:
case errors.Is(err, worker.ErrPoolFull):
    return errBusy
case errors.Is(err, worker.ErrPoolClosed):
    return errShuttingDown
}

Errors from jobs

A job's own error is returned unchanged by SubmitWait, futures, and groups — after all retries — so match it as you normally would. Two wrappers can appear around it:

Type	Created by	Notes
*PanicError	the pool, when a job panics	matches ErrJobPanic; Value and Stack hold the panic; unwraps to Value if it is an error
permanent error	worker.Permanent(err)	stops retries; transparent to errors.Is and errors.As

if perr, ok := errors.AsType[*worker.PanicError](err); ok {
    log.Printf("panic: %v\n%s", perr.Value, perr.Stack)
}

Context errors

Waiting operations return ctx.Err() — context.Canceled or context.DeadlineExceeded — when their context ends first:

• SubmitContext, SubmitWait, SubmitJobWait, RateLimiter.Submit, and Future.Await, when the caller's context ends,
• a job's result, when its attempt timed out on the last attempt, or its context was cancelled by the caller, a group, or a forced close.

Panics from constructors

NewTicker and NewRateLimiter panic on a non-positive interval or count, since those are programming errors. NewPool returns ErrInvalidConfig instead, because pool sizes often come from configuration.