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Is it OK to leave a Go channel open forever (never close the channel) if I never check for its state? Will it lead to memory leaks? Is the following code OK?

func (requestCh chan<- Request) GetResponse(data RequestData) Response {
    reply := make(chan Response)
    requestCh <- Request{data: data, replyCh: reply}
    return <-reply
}
peterSO
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Kluyg
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8 Answers8

402

It's OK to leave a Go channel open forever and never close it. When the channel is no longer used, it will be garbage collected.

Note that it is only necessary to close a channel if the receiver is looking for a close. Closing the channel is a control signal on the channel indicating that no more data follows.

Design Question: Channel Closing

peterSO
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    I'm not sure i agree with the response of the link. I had a memory leak in the 2GB range. As soon as I added the close the geyser became a trickle. – Richard Apr 01 '13 at 20:07
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    @Richard: Read the entire thread carefully. The author of Go `gc` and the author of `gccgo` say channel `close`s are not necessary, unless you are looking for a `close`. That's authoritative advice. – peterSO Apr 02 '13 at 06:05
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    Well if you have a buffered channel, adding messages to it should use memory. However if your channel is not buffered or nothing is added memory usage will not grow. – metakeule Aug 10 '14 at 17:02
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    What about this then: https://groups.google.com/forum/#!topic/golang-nuts/bfuwmhbZHYw ? – Kamil Dziedzic Aug 13 '14 at 10:04
  • @metakeule isn't the memory recycled after the channel is read (buffered channels) ? – hey Aug 29 '14 at 00:31
  • @hey I am not sure, but I think so. – metakeule Aug 30 '14 at 19:04
  • Buffered channels with buffered values also gets GC'd when not referenced anymore: http://grokbase.com/t/gg/golang-nuts/13agc3nssn/go-nuts-what-happens-to-buffered-channel-that-is-no-longer-being-read-from#20131016uod7mxxgmk6p6u52yirzumausm – HectorJ Nov 11 '15 at 10:17
  • this is also relevant: https://blog.golang.org/go-concurrency-patterns-timing-out-and (shows how to send to a channel without blocking, which is what you want in scenarios that are essentially "do N different things, and the first one to complete send something to this channel" or other such cases where goroutines may leak due to blocking) – Brad Peabody Nov 30 '16 at 11:36
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    True. But depending on how you coded your "channels logic", a goroutine can be blocked, and this will cause a huge memory leak. Read this: https://betterprogramming.pub/common-goroutine-leaks-that-you-should-avoid-fe12d12d6ee – Gabriel Arruda Dec 12 '22 at 12:46
  • I just spent a couple of hours troubleshooting a memory leak that was fixed by closing channels. As others have said, it's not _always_ OK to not close channels. A goroutine that is reading from a single channel will never be garbage collected until the channel is closed (even if the channel is empty). If the desired behaviour is to have such a goroutine garbage collected (i.e. to avoid a memory leak) then not closing the channel is not OK. – chris.redekop Sep 02 '23 at 15:11
61

Yes, it is ok to keep a channel open. As the go programming language book stated:

You needn't close every channel when you've finished with it. It's only necessary to close a channel when it is important to tell the receiving goroutines that all data have been sent. A channel that the garbage collector determinies to be unreachable will have its resources reclaimed whether or not it is closed. (Don't confuse this with the close operation for open files. It is important to call the Close method on every file when you've finished with it.)

xgord
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cizixs
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10

Yes, it's OK to leave the channel open, and in fact it is typical. A channel being open does not constitute a reference to the channel object, and so does not keep it from being garbage collected.

Sonia
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9

"One general principle of using Go channels is don't close a channel from the receiver side and don't close a channel if the channel has multiple concurrent senders."

As clearly mentioned in answer above that every channel will be GCed eventually once it is marked for cleanup, so it is okay to leave channel un-closed the only difference it will make is that that channel will be available for gc after a few cycles maybe if not closed explicitly.

Also the following articles this and this shows various ways to close a channel in case of 1:N, N:1 or M:N (senders:receivers)

Abhishek Srivastava
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8

This is very well covered above, however I find the following from A Tour of Go very clear, which also gives an example of when to close:

Another note: Channels aren't like files; you don't usually need to close them. Closing is only necessary when the receiver must be told there are no more values coming, such as to terminate a range loop.

user11809641
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1

It's not always OK. Leaving a channel open can cause memory leaks, depending on how you coded it.

Although GO is garbage collected, if a Goroutine that uses a channel for some reason is blocked (and leaving a channel open can be one of the reasons to the goroutine stay blocked), you will have a memory leak.

Here is a good article about the use of channels, goroutines, and how they are associated with most memory leaks problems in golang.

https://betterprogramming.pub/common-goroutine-leaks-that-you-should-avoid-fe12d12d6ee

Gabriel Arruda
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    Interesting, didn't know `data := <-ch` unblocks if ch never sends any data but gets closed. Turns out it just "sends" a default value for whatever type `data` is when closed. TIL. While this would help with avoiding gorouting leaks, it could cause logic issues if the goroutine assumes that "default data" was explicitly sent to the channel. This of course could be easily fixed by changing `data := <-ch` to `data, ok := <- ch; if ok { ...` but then you would remember to close the channel. Thanks for sharing! – Kluyg Dec 12 '22 at 18:28
0

Go is garbage collected, so you don't really have to 'free' anything.

There is possibility to close channels, but it's mostly used as - close(channel) - tell the goroutine (or main program) that nothing else will be sent on that channel.

Łukasz Gruner
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    AFAIK even in a garbage collected language a programmer is still responsible for freeing unmanaged resources, e.g. closing files, sockets and so one. Do I need to close the channel like a file? – Kluyg Dec 21 '11 at 17:32
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    @Kluyg The answer is no. You are talking about OS resources (which channels are not). It depends on a resource and language but usually it is recommended to close OS resources manually not because GC wouldn't do so but rather because it's nondeterministic. Most common related _gotcha_ is _too many open files_ error. You keep opening files... You expect GC to do so... You don't run out of memory (therefore GC doesn't kick in)... You run out of file descriptors at the OS level. OS kills the process :) – Pijusn Apr 14 '17 at 03:34
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    I'm confused about why this got so many downvotes while it was correct the whole time and states the same as other accepted answers... – eja Apr 16 '20 at 18:06
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If you will manually close the channel you are saving some task of garbage collector so saving some compute and speeding up your program a little bit.

Dheeraj Vishwakarma
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