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

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issues there are.

PR: 1096
This commit is contained in:
Richard Levitte 2005-06-18 05:52:16 +00:00
parent 4bd46774bb
commit eef468e330
1 changed files with 21 additions and 13 deletions
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34
doc/crypto/threads.pod
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@ -65,18 +65,10 @@ B<CRYPTO_LOCK>, and releases it otherwise.
B<file> and B<line> are the file number of the function setting the B<file> and B<line> are the file number of the function setting the
lock. They can be useful for debugging. lock. They can be useful for debugging.
id_function(void) is a function that returns a thread ID, for id_function(void) is a function that returns a thread ID, for example
instance, pthread_self(). It is not, needed on Windows nor on pthread_self() if it returns an integer (see NOTES below). It isn't
platforms where getpid() returns a different ID for each thread. needed on Windows nor on platforms where getpid() returns a different
However, even on those platforms, pthread_self() should be used, since ID for each thread (see NOTES below).
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.)
Additionally, OpenSSL supports dynamic locks, and sometimes, some parts Additionally, OpenSSL supports dynamic locks, and sometimes, some parts
of OpenSSL need it for better performance. To enable this, the following of OpenSSL need it for better performance. To enable this, the following
@ -133,7 +125,7 @@ CRYPTO_get_new_dynlockid() returns the index to the newly created lock.
The other functions return no values. The other functions return no values.
=head1 NOTE =head1 NOTES
You can find out if OpenSSL was configured with thread support: You can find out if OpenSSL was configured with thread support:
@ -148,6 +140,22 @@ You can find out if OpenSSL was configured with thread support:
Also, dynamic locks are currently not used internally by OpenSSL, but Also, dynamic locks are currently not used internally by OpenSSL, but
may do so in the future. 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 =head1 EXAMPLES
B<crypto/threads/mttest.c> shows examples of the callback functions on B<crypto/threads/mttest.c> shows examples of the callback functions on