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net: mention the cgo thread limit in package docs

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Updates #63978

Change-Id: I39a5c812b4f604baf4ca5ffcff52b8dc17d4990d
GitHub-Last-Rev: 4ab6e262f4
GitHub-Pull-Request: golang/go#63990
Reviewed-on: https://go-review.googlesource.com/c/go/+/539361
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
This commit is contained in:
Mateusz Poliwczak 2024-02-20 17:15:51 +00:00 committed by Gopher Robot
parent 67361bf868
commit 5a41204504
1 changed files with 6 additions and 2 deletions
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8
src/net/net.go
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@ -46,8 +46,8 @@ It can use a pure Go resolver that sends DNS requests directly to the servers
listed in /etc/resolv.conf, or it can use a cgo-based resolver that calls C listed in /etc/resolv.conf, or it can use a cgo-based resolver that calls C
library routines such as getaddrinfo and getnameinfo. library routines such as getaddrinfo and getnameinfo.
By default the pure Go resolver is used, because a blocked DNS request consumes On Unix the pure Go resolver is preferred over the cgo resolver, because a blocked DNS
only a goroutine, while a blocked C call consumes an operating system thread. request consumes only a goroutine, while a blocked C call consumes an operating system thread.
When cgo is available, the cgo-based resolver is used instead under a variety of When cgo is available, the cgo-based resolver is used instead under a variety of
conditions: on systems that do not let programs make direct DNS requests (OS X), conditions: on systems that do not let programs make direct DNS requests (OS X),
when the LOCALDOMAIN environment variable is present (even if empty), when the LOCALDOMAIN environment variable is present (even if empty),
@ -57,6 +57,10 @@ when /etc/resolv.conf or /etc/nsswitch.conf specify the use of features that the
Go resolver does not implement, and when the name being looked up ends in .local Go resolver does not implement, and when the name being looked up ends in .local
or is an mDNS name. or is an mDNS name.
On all systems (except Plan 9), when the cgo resolver is being used
this package applies a concurrent cgo lookup limit to prevent the system
from running out of system threads. Currently, it is limited to 500 concurrent lookups.
The resolver decision can be overridden by setting the netdns value of the The resolver decision can be overridden by setting the netdns value of the
GODEBUG environment variable (see package runtime) to go or cgo, as in: GODEBUG environment variable (see package runtime) to go or cgo, as in: