+threadid_func(CRYPTO_THREADID *id) is needed to record the currently-executing
+thread's identifier into B<id>. The implementation of this callback should not
+fill in B<id> directly, but should use CRYPTO_THREADID_set_numeric() if thread
+IDs are numeric, or CRYPTO_THREADID_set_pointer() if they are pointer-based.
+If the application does not register such a callback using
+CRYPTO_THREADID_set_callback(), then a default implementation is used - on
+Windows and BeOS this uses the system's default thread identifying APIs, and on
+all other platforms it uses the address of B<errno>. The latter is satisfactory
+for thread-safety if and only if the platform has a thread-local error number
+facility.
+
+Once threadid_func() is registered, or if the built-in default implementation is
+to be used;
+
+=over 4
+
+=item *
+CRYPTO_THREADID_current() records the currently-executing thread ID into the
+given B<id> object.
+
+=item *
+CRYPTO_THREADID_cmp() compares two thread IDs (returning zero for equality, ie.
+the same semantics as memcmp()).
+
+=item *
+CRYPTO_THREADID_cpy() duplicates a thread ID value,
+
+=item *
+CRYPTO_THREADID_hash() returns a numeric value usable as a hash-table key. This
+is usually the exact numeric or pointer-based thread ID used internally, however
+this also handles the unusual case where pointers are larger than 'long'
+variables and the platform's thread IDs are pointer-based - in this case, mixing
+is done to attempt to produce a unique numeric value even though it is not as
+wide as the platform's true thread IDs.
+
+=back
+
+Additionally, OpenSSL supports dynamic locks, and sometimes, some parts
+of OpenSSL need it for better performance. To enable this, the following
+is required:
+
+=over 4
+
+=item *
+Three additional callback function, dyn_create_function, dyn_lock_function
+and dyn_destroy_function.
+
+=item *
+A structure defined with the data that each lock needs to handle.
+
+=back
+
+struct CRYPTO_dynlock_value has to be defined to contain whatever structure
+is needed to handle locks.
+
+dyn_create_function(const char *file, int line) is needed to create a
+lock. Multi-threaded applications might crash at random if it is not set.
+
+dyn_lock_function(int mode, CRYPTO_dynlock *l, const char *file, int line)
+is needed to perform locking off dynamic lock numbered n. Multi-threaded
+applications might crash at random if it is not set.
+
+dyn_destroy_function(CRYPTO_dynlock *l, const char *file, int line) is
+needed to destroy the lock l. Multi-threaded applications might crash at
+random if it is not set.
+
+CRYPTO_get_new_dynlockid() is used to create locks. It will call
+dyn_create_function for the actual creation.
+
+CRYPTO_destroy_dynlockid() is used to destroy locks. It will call
+dyn_destroy_function for the actual destruction.
+
+CRYPTO_lock() is used to lock and unlock the locks. mode is a bitfield
+describing what should be done with the lock. n is the number of the
+lock as returned from CRYPTO_get_new_dynlockid(). mode can be combined
+from the following values. These values are pairwise exclusive, with
+undefined behaviour if misused (for example, CRYPTO_READ and CRYPTO_WRITE
+should not be used together):
+
+ CRYPTO_LOCK 0x01
+ CRYPTO_UNLOCK 0x02
+ CRYPTO_READ 0x04
+ CRYPTO_WRITE 0x08