threads(3) | OpenSSL | threads(3) |
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 n-th lock if mode & CRYPTO_LOCK, and releases it otherwise.
file and line are the file number of the function setting the lock. They can be useful for debugging.
threadid_func(CRYPTO_THREADID *id) is needed to record the currently-executing thread's identifier into id. The implementation of this callback should not fill in 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 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;
• | CRYPTO_THREADID_current() records the currently-executing thread ID into the given id object. |
• | CRYPTO_THREADID_cmp() compares two thread IDs (returning zero for equality, ie. the same semantics as memcmp()). |
• | CRYPTO_THREADID_cpy() duplicates a thread ID value, |
• | 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. |
Additionally, OpenSSL supports dynamic locks, and sometimes, some parts of OpenSSL need it for better performance. To enable this, the following is required:
• | Three additional callback function, dyn_create_function, dyn_lock_function and dyn_destroy_function. |
• | A structure defined with the data that each lock needs to handle. |
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
CRYPTO_get_new_dynlockid() returns the index to the newly created lock.
The other functions return no values.
#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.
January 6, 2010 | 1.0.1-dev |