flag: IsBoolFlag hides errors #9345
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Nov 8, 2015
This change is the same as CL #9345 which was reverted, except for a small bug fix. The only change is to the body of sendDirect and its callsite. Also added a test. The problem was during a channel send operation. The target of the send was a sleeping goroutine waiting to receive. We basically do: 1) Read the destination pointer out of the sudog structure 2) Copy the value we're sending to that destination pointer Unfortunately, the previous change had a goroutine suspend point between 1 & 2 (the call to sendDirect). At that point the destination goroutine's stack could be copied (shrunk). The pointer we read in step 1 is no longer valid for step 2. Fixed by not allowing any suspension points between 1 & 2. I suspect the old code worked correctly basically by accident. Fixes #13169 The original 9345: This change removes the retry mechanism we use for buffered channels. Instead, any sender waking up a receiver or vice versa completes the full protocol with its counterpart. This means the counterpart does not need to relock the channel when it wakes up. (Currently buffered channels need to relock on wakeup.) For sends on a channel with waiting receivers, this change replaces two copies (sender->queue, queue->receiver) with one (sender->receiver). For receives on channels with a waiting sender, two copies are still required. This change unifies to a large degree the algorithm for buffered and unbuffered channels, simplifying the overall implementation. Fixes #11506 Change-Id: I57dfa3fc219cffa4d48301ee15fe5479299efa09 Reviewed-on: https://go-review.googlesource.com/16740 Reviewed-by: Ian Lance Taylor <iant@golang.org>
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Consider the following piece of code: http://play.golang.org/p/A63iWciutA
When implementing a custom
flag.Valuethat is a bool flag, any errors fromSetwill be discarded if the flag is set without an explicit value. This makes it impossible to return an error if a flag is provided multiple times, or to implement a set of mutually exclusive boolean flags, backed by a single flag.Value.go version go1.4 linux/amd64
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