To perform writes in AioSocketChannel, we get a ByteBuffer view of the
outbound buffer and specify it as a parameter when we call
AsynchronousSocketChannel.write().
In most cases, the write() operation is finished immediately. However,
sometimes, it is scheduled for later execution. In such a case, there's
a chance for a user's handler to append more data to the outbound
buffer.
When more data is appended to the outbound buffer, the outbound buffer
can expand its capacity by itself. Changing the capacity of a buffer is
basically made of the following steps:
1. Allocate a larger new internal memory region.
2. Copy the current content of the buffer to the new memory region.
3. Rewire the buffer so that it refers to the new region.
4. Deallocate the old memory region.
Because the old memory region is deallocated at the step 4, the write
operation scheduled later will access the deallocated region, leading
all sort of data corruption or even segfaults.
To prevent this situation, I added suspendIntermediaryDeallocations()
and resumeIntermediaryDeallocations() to UnsafeByteBuf.
AioSocketChannel.doFlushByteBuf() now calls suspendIntermediaryDealloc()
to defer the deallocation of the old memory regions until the completion
handler is notified.
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