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28 July 2008

My Arrogance in Finding Bugs

Last night I discovered this piece of code (simplified version):

private void Foo()
bool b = false;
new Thread((ThreadStart)delegate { b = true;}).Start();

private void WaitForBool(bool b)
while (!b)

I was immediately filled with disgust. How could someone write such a function (WaitForBool), which is one big bug? Of course the waiting will never be over, because bool is a value type, and no external influence can modify its value.

Later, I realized the fool is me.

I ran into this code a while back, and it did have a "ref" bool, which means it can be modified by the external thread. Resharper helpfully displayed a tip "this parameter can be declared as a value" , which I took without thinking too much about the consequences (I trust Resharper too much sometimes, it appears). So I deleted the "ref" with Resharper's help and created the bug myself without noticing.

(As a side note, of course this method of waiting for a bool should never be used - use ManualResetEvent instead).

Fixed in the next Resharper build (Resharper 4.0.1, build 913), within a few hours of reporting it. Cool.

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