fix race condition in opening named pipes #196
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Opening a read-only or write-only pipe blocks until a pipe with
opposite access or a read-write pipe is opened.
The old implementation had the following race-condition:
1. Open a read-only pipe.
2. Check if there's a write-only or read-write pipe.
a) No, there isn't, so this blocks.
3. Open a write-only or read-write pipe.
a) This doesn't block because there's already a read-only pipe
waiting.
4. Notify the read-only pipe so that it can redo the check from step 2.
5. Close the pipe from step 3.
6. The read-only pipe receives the notification and checks again.
a) There aren't any write-only/read-write pipes alive right now, so
open continues to block.
Opening a read-only pipe should succeed when a write-only/read-write
pipe is opened even when that pipe is already closed by the time
opening the read-only pipe finishes.
This didn't apply just to read-only pipes, but also write-only pipes.
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Opening a read-only or write-only pipe blocks until a pipe with opposite access or a read-write pipe is opened.
The old implementation had the following race-condition:
Opening a read-only pipe should succeed when a write-only/read-write pipe is opened even when that pipe is already closed by the time opening the read-only pipe finishes.
This didn't apply just to read-only pipes, but also write-only pipes.