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diff --git a/openssl/doc/crypto/threads.pod b/openssl/doc/crypto/threads.pod
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@@ -0,0 +1,175 @@
+=pod
+
+=head1 NAME
+
+CRYPTO_set_locking_callback, CRYPTO_set_id_callback, CRYPTO_num_locks,
+CRYPTO_set_dynlock_create_callback, CRYPTO_set_dynlock_lock_callback,
+CRYPTO_set_dynlock_destroy_callback, CRYPTO_get_new_dynlockid,
+CRYPTO_destroy_dynlockid, CRYPTO_lock - OpenSSL thread support
+
+=head1 SYNOPSIS
+
+ #include <openssl/crypto.h>
+
+ void CRYPTO_set_locking_callback(void (*locking_function)(int mode,
+        int n, const char *file, int line));
+
+ void CRYPTO_set_id_callback(unsigned long (*id_function)(void));
+
+ int CRYPTO_num_locks(void);
+
+
+ /* struct CRYPTO_dynlock_value needs to be defined by the user */
+ struct CRYPTO_dynlock_value;
+
+ void CRYPTO_set_dynlock_create_callback(struct CRYPTO_dynlock_value *
+	(*dyn_create_function)(char *file, int line));
+ void CRYPTO_set_dynlock_lock_callback(void (*dyn_lock_function)
+	(int mode, struct CRYPTO_dynlock_value *l,
+	const char *file, int line));
+ void CRYPTO_set_dynlock_destroy_callback(void (*dyn_destroy_function)
+	(struct CRYPTO_dynlock_value *l, const char *file, int line));
+
+ int CRYPTO_get_new_dynlockid(void);
+
+ void CRYPTO_destroy_dynlockid(int i);
+
+ void CRYPTO_lock(int mode, int n, const char *file, int line);
+
+ #define CRYPTO_w_lock(type)	\
+	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
+ #define CRYPTO_w_unlock(type)	\
+	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_WRITE,type,__FILE__,__LINE__)
+ #define CRYPTO_r_lock(type)	\
+	CRYPTO_lock(CRYPTO_LOCK|CRYPTO_READ,type,__FILE__,__LINE__)
+ #define CRYPTO_r_unlock(type)	\
+	CRYPTO_lock(CRYPTO_UNLOCK|CRYPTO_READ,type,__FILE__,__LINE__)
+ #define CRYPTO_add(addr,amount,type)	\
+	CRYPTO_add_lock(addr,amount,type,__FILE__,__LINE__)
+
+=head1 DESCRIPTION
+
+OpenSSL can safely be used in multi-threaded applications provided
+that at least two callback functions are set.
+
+locking_function(int mode, int n, const char *file, int line) is
+needed to perform locking on shared data structures. 
+(Note that OpenSSL uses a number of global data structures that
+will be implicitly shared whenever multiple threads use OpenSSL.)
+Multi-threaded applications will crash at random if it is not set.
+
+locking_function() must be able to handle up to CRYPTO_num_locks()
+different mutex locks. It sets the B<n>-th lock if B<mode> &
+B<CRYPTO_LOCK>, and releases it otherwise.
+
+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 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
+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
+
+=head1 RETURN VALUES
+
+CRYPTO_num_locks() returns the required number of locks.
+
+CRYPTO_get_new_dynlockid() returns the index to the newly created lock.
+
+The other functions return no values.
+
+=head1 NOTES
+
+You can find out if OpenSSL was configured with thread support:
+
+ #define OPENSSL_THREAD_DEFINES
+ #include <openssl/opensslconf.h>
+ #if defined(OPENSSL_THREADS)
+   // thread support enabled
+ #else
+   // no thread support
+ #endif
+
+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
+Solaris, Irix and Win32.
+
+=head1 HISTORY
+
+CRYPTO_set_locking_callback() and CRYPTO_set_id_callback() are
+available in all versions of SSLeay and OpenSSL.
+CRYPTO_num_locks() was added in OpenSSL 0.9.4.
+All functions dealing with dynamic locks were added in OpenSSL 0.9.5b-dev.
+
+=head1 SEE ALSO
+
+L<crypto(3)|crypto(3)>
+
+=cut