Add Thread Specific Data (TSD) Implementation

Thread specific data has implemented using a hash table, this avoids
the need to add a member to the task structure and allows maximum
portability between kernels.  This implementation has been optimized
to keep the tsd_set() and tsd_get() times as small as possible.

The majority of the entries in the hash table are for specific tsd
entries.  These entries are hashed by the product of their key and
pid because by design the key and pid are guaranteed to be unique.
Their product also has the desirable properly that it will be uniformly
distributed over the hash bins providing neither the pid nor key is zero.
Under linux the zero pid is always the init process and thus won't be
used, and this implementation is careful to never to assign a zero key.
By default the hash table is sized to 512 bins which is expected to
be sufficient for light to moderate usage of thread specific data.

The hash table contains two additional type of entries.  They first
type is entry is called a 'key' entry and it is added to the hash during
tsd_create().  It is used to store the address of the destructor function
and it is used as an anchor point.  All tsd entries which use the same
key will be linked to this entry.  This is used during tsd_destory() to
quickly call the destructor function for all tsd associated with the key.
The 'key' entry may be looked up with tsd_hash_search() by passing the
key you wish to lookup and DTOR_PID constant as the pid.

The second type of entry is called a 'pid' entry and it is added to the
hash the first time a process set a key.  The 'pid' entry is also used
as an anchor and all tsd for the process will be linked to it.  This
list is using during tsd_exit() to ensure all registered destructors
are run for the process.  The 'pid' entry may be looked up with
tsd_hash_search() by passing the PID_KEY constant as the key, and
the process pid.  Note that tsd_exit() is called by thread_exit()
so if your using the Solaris thread API you should not need to call
tsd_exit() directly.

2 files changed, 46 insertions, 0 deletions

diff --git a/include/sys/thread.h b/include/sys/thread.h
index 06db6d4c9..c5f4234da 100644
--- a/include/sys/thread.h
+++ b/include/sys/thread.h
@@ -31,6 +31,7 @@
 #include <linux/kthread.h>
 #include <sys/types.h>
 #include <sys/sysmacros.h>
+#include <sys/tsd.h>
 
 /*
  * Thread interfaces
diff --git a/include/sys/tsd.h b/include/sys/tsd.h
new file mode 100644
index 000000000..56f3b4cd8
--- /dev/null
+++ b/include/sys/tsd.h
@@ -0,0 +1,45 @@
+/*****************************************************************************\
+ *  Copyright (C) 2010 Lawrence Livermore National Security, LLC.
+ *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
+ *  Written by Brian Behlendorf <[email protected]>.
+ *  UCRL-CODE-235197
+ *
+ *  This file is part of the SPL, Solaris Porting Layer.
+ *  For details, see <http://github.com/behlendorf/spl/>.
+ *
+ *  The SPL is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License as published by the
+ *  Free Software Foundation; either version 2 of the License, or (at your
+ *  option) any later version.
+ *
+ *  The SPL is distributed in the hope that it will be useful, but WITHOUT
+ *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ *  for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
+\*****************************************************************************/
+
+#ifndef _SPL_TSD_H
+#define _SPL_TSD_H
+
+#include <sys/types.h>
+
+#define TSD_HASH_TABLE_BITS_DEFAULT	9
+#define TSD_KEYS_MAX			32768
+#define DTOR_PID			(PID_MAX_LIMIT+1)
+#define PID_KEY				(TSD_KEYS_MAX+1)
+
+typedef void (*dtor_func_t)(void *);
+
+extern int tsd_set(uint_t, void *);
+extern void *tsd_get(uint_t);
+extern void tsd_create(uint_t *, dtor_func_t);
+extern void tsd_destroy(uint_t *);
+extern void tsd_exit(void);
+
+int tsd_init(void);
+void tsd_fini(void);
+
+#endif /* _SPL_TSD_H */