ovs-thread: New function ovsthread_id_self().

I foresee a need for possibly large numbers of instances of "struct
seq" (which is introduced in an upcoming patch).  Each struct seq
needs some per-thread data.  POSIX has pthread_key_t for this, but
the number of keys can be fairly limited, to as few as 128.  It is
reasonable to work around this by using a hash table indexed on the
current thread.  That only works if one can get a thread identifier
that is hashable (pthread_t is not).  This patch introduces a
hashable thread identifier.

Signed-off-by: Ben Pfaff <blp@nicira.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/ovs-thread.h b/lib/ovs-thread.h
index abe479ae6..e644832b2 100644
--- a/lib/ovs-thread.h
+++ b/lib/ovs-thread.h
@@ -501,6 +501,23 @@ ovsthread_once_start(struct ovsthread_once *once)
     ((ONCE)->done ? false : ({ OVS_MACRO_LOCK((&ONCE->mutex)); true; }))
 #endif
 
+/* Thread ID.
+ *
+ * pthread_t isn't so nice for some purposes.  Its size and representation are
+ * implementation dependent, which means that there is no way to hash it.
+ * This thread ID avoids the problem.
+ */
+
+DECLARE_EXTERN_PER_THREAD_DATA(unsigned int, ovsthread_id);
+
+/* Returns a per-thread identifier unique within the lifetime of the
+ * process. */
+static inline unsigned int
+ovsthread_id_self(void)
+{
+    return *ovsthread_id_get();
+}
+
 void assert_single_threaded_at(const char *where);
 #define assert_single_threaded() assert_single_threaded_at(SOURCE_LOCATOR)