openssl/doc/crypto/threads.pod
Geoff Thorpe f7ccba3edf There was a need to support thread ID types that couldn't be reliably cast
to 'unsigned long' (ie. odd platforms/compilers), so a pointer-typed
version was added but it required portable code to check *both* modes to
determine equality. This commit maintains the availability of both thread
ID types, but deprecates the type-specific accessor APIs that invoke the
callbacks - instead a single type-independent API is used.  This simplifies
software that calls into this interface, and should also make it less
error-prone - as forgetting to call and compare *both* thread ID accessors
could have led to hard-to-debug/infrequent bugs (that might only affect
certain platforms or thread implementations). As the CHANGES note says,
there were corresponding deprecations and replacements in the
thread-related functions for BN_BLINDING and ERR too.
2008-03-28 02:49:43 +00:00

189 lines
6.6 KiB
Text

=pod
=head1 NAME
CRYPTO_set_locking_callback, CRYPTO_set_id_callback,
CRYPTO_set_idptr_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));
void CRYPTO_set_idptr_callback(void *(*idptr_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 numerical thread ID,
for example pthread_self() if it returns an integer (see NOTES below).
By OpenSSL's defaults, this is not needed on Windows nor on platforms
where getpid() returns a different ID for each thread (see NOTES
below).
idptr_function(void) is a function that similarly returns a thread ID,
but of type void *. This is not needed on platforms where &errno is
different for each thread.
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. It is for cases like this that
CRYPTO_set_idptr_callback() comes in handy. (E.g., call malloc(1)
once in each thread, and have idptr_function() return a pointer to
this object.) Note that if neither id_function() or idptr_function()
are provided, OpenSSL will use (&errno) as a fallback (as this
usually returns a unique address for each thread).
=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.
CRYPTO_set_idptr_callback() was added in OpenSSL 0.9.9.
=head1 SEE ALSO
L<crypto(3)|crypto(3)>
=cut