The value of PTHREAD_DESTRUCTOR_ITERATIONS is
provided by the
CYGNUM_POSIX_PTHREAD_DESTRUCTOR_ITERATIONS
option. This controls the number of times that a key destructor
will be called while the data item remains non-NULL.
The value of PTHREAD_KEYS_MAX is provided
by the CYGNUM_POSIX_PTHREAD_KEYS_MAX
option. This defines the maximum number of per-thread data items
supported. The POSIX standard calls for this to be a minimum of
128, which is rather large for an embedded system. The default
value for this option is set to 128 for compatibility but it
should be reduced to a more usable value.