CBCharacteristic update value may lose due to asynchronous call on main queue

[coupgar]

In the cbperiphral delegate callback, i.e. peripheral:didUpdateValueForCharacteristic:error, you call the notifyCharacteristicHandler:error handler on the main queue, however, the value of CBCharacteristic may have changed by the time main queue come back.

Other call back on the main queue may have same issue. related file is YMSCBPeripheral.m

[kickingvegas]

Will investigate.

[kickingvegas]

FWIW, there are a whole host of changes coming to callback handling when I get the cycles to put them in.

[jaysonjh]

i hit the same issue，i moved the main queue code to delegate code line：
__weak YMSCBPeripheral *this = self;
YMSCBService *btService = [this findService:characteristic.service];
YMSCBCharacteristic *yc = [btService findCharacteristic:characteristic];
if (yc.cbCharacteristic.isNotifying) {
[btService notifyCharacteristicHandler:yc error:error];

} else {
    if ([yc.readCallbacks count] > 0) {
        [yc executeReadCallback:characteristic.value error:error];
    }
}
_YMS_PERFORM_ON_MAIN_THREAD(^{
    if ([this.delegate respondsToSelector:@selector(peripheral:didUpdateValueForCharacteristic:error:)]) {
        [this.delegate peripheral:peripheral didUpdateValueForCharacteristic:characteristic error:error];
    }
});

And then update value is ok.

[jaysonjh]

YmsCoreBluetooth lib stop updated？

[kickingvegas]

@jaysonjh Nope, but been put into a longer hiatus than I expected due to work issues. There's a lot I'd like to change given my working with this codebase for some time. In particular, the changes made with respect to this issue is recognizing that YMSCoreBluetooth is trying too hard to push stuff back on the main queue in the delegate methods. Changing the code base to stop doing this will definitely break existing installs and when that happens, then all kinds of design decisions in this framework are open for review.

[jimneylee]

Today I have the same problem, solved it just make thead sleep 0.01s. not a good way BUT minimum change.

    _YMS_PERFORM_ON_MAIN_THREAD(^{
      // ......
    });
    [NSThread sleepForTimeInterval:0.01];

[jimneylee]

when log the data, I found the reason:
didUpdateValueForCharacteristic
update data = <202d>
update data = <39000000 000000>
update data = <31780a>
update data = <3d0000>

in main thread, got the data as follow:
parse data = <3d0000>
parse data = <3d0000>
parse data = <3d0000>
parse data = <3d0000>

if in one cycle, received four values, then in main thread, they are same to last value(3d0000), I think the reason is that all the points of characteristic is pointing at last one.