With the recent merging of embedded package imports and the entry CLI
package, it is now possible for users to build in mcl code into a single
binary. This additional permission makes it explicitly clear that this
is permitted to make it easier for those users. The condition is phrased
so that the terms can be "patched" by the original author if it's
necessary for the project. For example, if the name of the language
(mcl) changes, has a differently named new version, someone finds a
phrasing improvement or a legal loophole, or for some other
reasonable circumstance. Now go write some beautiful embedded tools!
If our machine has that pipe busy, don't panic the test. (We do want it
to fail though!)
We're also more careful to check nil object just as a convenience to
help programmers.
After some investigation, it appears that SocketSet.Shutdown() and
SocketSet.Close() are not synchronous operations. The sendto system call
called in SocketSet.Shutdown() is not a blocking send. That means there
is a race in which SocketSet.Shutdown() sends a message to a file
descriptor to unblock select, while SocketSet.Close() will close the
file descriptor that the message is being sent to. If SocketSet.Close()
wins the race, select is listening on a dead file descriptor and will
hang indefinitely.
This is fixed in the current master by putting SocketSet.Close() inside
of the goroutine in which data from the socket is being received. It
relies on SocketSet.Shutdown() being called to terminate the goroutine.
While this works most of the time, there is a race here. All the
goroutines can also be terminated by a closeChan. If the goroutine
receives an event (thus unblocking select) and then closeChan is
triggered, both SocketSet.Shutdown() and SocketSet.Close() race, leading
to undefined behavior.
This patch ensures the ordering of the two function calls by pulling
them both out of the goroutine and separating them with a WaitGroup.
Co-authored-by: James Shubin <james@shubin.ca>
Test to ensure that SocketSet is nonblocking and will close when
SocketSet.Shutdown() is called. Create a SocketSet that will never
receive any data and leave it running in a goroutine with a WaitGroup
for a second. If Shutdown is working correctly, the goroutine will be
terminated after the timer expires.
