0bcb822e5b
This commit simplifies device state management. It creates a single unified state variable and documents its semantics. It also makes state changes more atomic. As an example of the sort of bug that occurred due to non-atomic state changes, the following sequence of events used to occur approximately every 2.5 million test runs: * RoutineTUNEventReader received an EventDown event. * It called device.Down, which called device.setUpDown. * That set device.state.changing, but did not yet attempt to lock device.state.Mutex. * Test completion called device.Close. * device.Close locked device.state.Mutex. * device.Close blocked on a call to device.state.stopping.Wait. * device.setUpDown then attempted to lock device.state.Mutex and blocked. Deadlock results. setUpDown cannot progress because device.state.Mutex is locked. Until setUpDown returns, RoutineTUNEventReader cannot call device.state.stopping.Done. Until device.state.stopping.Done gets called, device.state.stopping.Wait is blocked. As long as device.state.stopping.Wait is blocked, device.state.Mutex cannot be unlocked. This commit fixes that deadlock by holding device.state.mu when checking that the device is not closed. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
27 lines
737 B
Go
27 lines
737 B
Go
// Code generated by "stringer -type deviceState -trimprefix=deviceState"; DO NOT EDIT.
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package device
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import "strconv"
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func _() {
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// An "invalid array index" compiler error signifies that the constant values have changed.
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// Re-run the stringer command to generate them again.
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var x [1]struct{}
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_ = x[deviceStateNew-0]
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_ = x[deviceStateDown-1]
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_ = x[deviceStateUp-2]
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_ = x[deviceStateClosed-3]
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}
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const _deviceState_name = "NewDownUpClosed"
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var _deviceState_index = [...]uint8{0, 3, 7, 9, 15}
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func (i deviceState) String() string {
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if i >= deviceState(len(_deviceState_index)-1) {
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return "deviceState(" + strconv.FormatInt(int64(i), 10) + ")"
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}
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return _deviceState_name[_deviceState_index[i]:_deviceState_index[i+1]]
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}
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