My reflex when seeing go f() was to translate it into “start a thread.” That translation is convenient and wrong enough to cause bad designs.
A goroutine is a language-level activity scheduled by the Go runtime. Its initial stack is small and can grow, so creating thousands is practical in cases where creating thousands of pthreads would be a conversation with both the kernel and the person carrying the pager.
I tested this with a deliberately dull program:
package main
import "fmt"
func wait(done chan bool) {
done <- true
}
func main() {
done := make(chan bool)
for i := 0; i < 10000; i++ {
go wait(done)
}
for i := 0; i < 10000; i++ {
<-done
}
fmt.Println("finished")
}
The channel is doing two jobs: carrying a value and synchronizing sender with receiver. With an unbuffered channel, the send waits for a receive. The program does not need a mutex around a shared completion counter.
That does not make races impossible. If all those goroutines update the same map, I still have a race. “Do not communicate by sharing memory” is good direction, not a force field.
The early runtime is another caveat. On the snapshot I used, scheduling and stack management are active work. Timing results vary, and a tight goroutine that never calls into the runtime can be an unfriendly neighbor. I would not build a latency promise from this experiment.
The cheap creation cost also does not excuse leaving goroutines blocked forever. Their stacks are small, not imaginary, and their work still needs a defined end.
What I do like is the change in scale. In C, a thread is sufficiently costly and awkward that I first ask how to avoid one. In Go, I can model each independent operation directly, then decide where synchronization belongs. The runtime may multiplex many goroutines over fewer operating-system threads; that implementation is precisely why “goroutine equals pthread” is a poor mental model.
This is not magic parallelism either. More runnable work does not create more processors, and today’s defaults may use only one. It does make concurrency cheap enough to express before I optimize it. For server and pipeline code, that changes the first sketch substantially.
