Add better documentation on how id_function() should be defined and what

B<file> and B<line> are the file number of the function setting the

lock. They can be useful for debugging.

id_function(void) is a function that returns a thread ID, for

instance, pthread_self(). It is not, needed on Windows nor on

platforms where getpid() returns a different ID for each thread.

However, even on those platforms, pthread_self() should be used, since

the behavior of getpid() may depend on the machine where the program

is being run, not the machine where the program is being compiled.

(For instance, Red Hat 8 Linux and earlier used LinuxThreads, whose

getpid() returns a different value for each thread; Red Hat 9 Linux

and later use NPTL, which is Posix-conformant, and thus whose getpid()

returns the same value for all threads in a process.  But a program

compiled on Red Hat 8 and run on Red Hat 9 will by default see

getpid() returning the same value for all threads.)

id_function(void) is a function that returns a thread ID, for example

pthread_self() if it returns an integer (see NOTES below).  It isn't

needed on Windows nor on platforms where getpid() returns a different

ID for each thread (see NOTES below).

Additionally, OpenSSL supports dynamic locks, and sometimes, some parts

of OpenSSL need it for better performance.  To enable this, the following

The other functions return no values.

=head1 NOTE

=head1 NOTES

You can find out if OpenSSL was configured with thread support:

Also, dynamic locks are currently not used internally by OpenSSL, but

may do so in the future.

Defining id_function(void) has it's own issues.  Generally speaking,

pthread_self() should be used, even on platforms where getpid() gives

different answers in each thread, since that may depend on the machine

the program is run on, not the machine where the program is being

compiled.  For instance, Red Hat 8 Linux and earlier used

LinuxThreads, whose getpid() returns a different value for each

thread.  Red Hat 9 Linux and later use NPTL, which is

Posix-conformant, and has a getpid() that returns the same value for

all threads in a process.  A program compiled on Red Hat 8 and run on

Red Hat 9 will therefore see getpid() returning the same value for

all threads.

There is still the issue of platforms where pthread_self() returns

something other than an integer.  This is a bit unusual, and this

manual has no cookbook solution for that case.

=head1 EXAMPLES

B<crypto/threads/mttest.c> shows examples of the callback functions on