Can now specify a safe encoding which prevents segfaults in containers. Fixes #1

[mikegleasonjr]

The feature is opt-in. The default behaviour is the current behaviour.

Here are the benchmarks:

BenchmarkSafeEncoding-4      	      20	  90524720 ns/op	 2990679 B/op	     325 allocs/op
BenchmarkRegularEncoding-4   	      20	  86883378 ns/op	  427743 B/op	     318 allocs/op

Fixes #1

[jdeng]

thanks!

[snowlock650]

@mikegleasonjr I have encountered the same error as in [https://github.com//issues/15]( issue 15 ). It is resolved with Safe encoding fix; I have read your patch but don't understand why it prevents the crash?

I understand that C.GoBytes allocates the memory and copies the content of byte pointer to ycc.Y (for example)
and (*[1 << 30]byte)(unsafe.Pointer(y))[:int(height)*int(ystride)] simply assign the pointer to the slice struct.

But I don't see why would the second statement causes SIGSEGV? If the memory to the said pointer is invalid, then both operation should fail?

[rajendraventurit]

@mikegleasonjr I am still facing the segfault in containers. Any help would be appreciable.

[mikegleasonjr]

The code was provided for me by the original author. In fact, I think there was 2 code blocks, one commented out and one active, and we put them behind a flag if my memory serves me correctly to be able to switch between the two at runtime and prevent segfaults in containers.

Sorry I can't be of any more help...

[rajendraventurit]

The code was provided for me by the original author. In fact, I think there was 2 code blocks, one commented out and one active, and we put them behind a flag if my memory serves me correctly to be able to switch between the two at runtime and prevent segfaults in containers.

Sorry I can't be of any more help...

Added the flag and it worked. Thanks!