void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
void xpthread_create(pthread_t *, pthread_attr_t *, void *(*)(void *), void *);
+\f
+/* Per-thread data.
+ *
+ * Multiple forms of per-thread data exist, each with its own pluses and
+ * minuses:
+ *
+ * - POSIX per-thread data via pthread_key_t is portable to any pthreads
+ * implementation, and allows a destructor function to be defined. It
+ * only (directly) supports per-thread pointers, which are always
+ * initialized to NULL. It requires once-only allocation of a
+ * pthread_key_t value. It is relatively slow.
+ *
+ * - The thread_local feature newly defined in C11 <threads.h> works with
+ * any data type and initializer, and it is fast. thread_local does not
+ * require once-only initialization like pthread_key_t. C11 does not
+ * define what happens if one attempts to access a thread_local object
+ * from a thread other than the one to which that object belongs. There
+ * is no provision to call a user-specified destructor when a thread
+ * ends.
+ *
+ * - The __thread keyword is a GCC extension similar to thread_local but
+ * with a longer history. __thread is not portable to every GCC version
+ * or environment. __thread does not restrict the use of a thread-local
+ * object outside its own thread.
+ *
+ * Here's a handy summary:
+ *
+ * pthread_key_t thread_local __thread
+ * ------------- ------------ -------------
+ * portability high low medium
+ * speed low high high
+ * supports destructors? yes no no
+ * needs key allocation? yes no no
+ * arbitrary initializer? no yes yes
+ * cross-thread access? yes no yes
+ */
+
+/* DEFINE_PER_THREAD_DATA(TYPE, NAME, INITIALIZER).
+ *
+ * One should prefer to use POSIX per-thread data, via pthread_key_t, when its
+ * performance is acceptable, because of its portability (see the table above).
+ * This macro is an alternatives that takes advantage of thread_local (and
+ * __thread), for its performance, when it is available, and falls back to
+ * POSIX per-thread data otherwise.
+ *
+ * Defines per-thread variable NAME with the given TYPE, initialized to
+ * INITIALIZER (which must be valid as an initializer for a variable with
+ * static lifetime).
+ *
+ * The public interface to the variable is:
+ *
+ * TYPE *NAME_get(void)
+ * TYPE *NAME_get_unsafe(void)
+ *
+ * Returns the address of this thread's instance of NAME.
+ *
+ * Use NAME_get() in a context where this might be the first use of the
+ * per-thread variable in the program. Use NAME_get_unsafe(), which
+ * avoids a conditional test and is thus slightly faster, in a context
+ * where one knows that NAME_get() has already been called previously.
+ *
+ * There is no "NAME_set()" (or "NAME_set_unsafe()") function. To set the
+ * value of the per-thread variable, dereference the pointer returned by
+ * TYPE_get() or TYPE_get_unsafe(), e.g. *TYPE_get() = 0.
+ */
+#if HAVE_THREAD_LOCAL || HAVE___THREAD
+
+#if HAVE_THREAD_LOCAL
+#include <threads.h>
+#elif HAVE___THREAD
+#define thread_local __thread
+#else
+#error
+#endif
+
+#define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
+ typedef TYPE NAME##_type; \
+ static thread_local NAME##_type NAME##_var = __VA_ARGS__; \
+ \
+ static NAME##_type * \
+ NAME##_get_unsafe(void) \
+ { \
+ return &NAME##_var; \
+ } \
+ \
+ static NAME##_type * \
+ NAME##_get(void) \
+ { \
+ return NAME##_get_unsafe(); \
+ }
+#else /* no C implementation support for thread-local storage */
+#define DEFINE_PER_THREAD_DATA(TYPE, NAME, ...) \
+ typedef TYPE NAME##_type; \
+ static pthread_key_t NAME##_key; \
+ \
+ static NAME##_type * \
+ NAME##_get_unsafe(void) \
+ { \
+ return pthread_getspecific(NAME##_key); \
+ } \
+ \
+ static void \
+ NAME##_once_init(void) \
+ { \
+ if (pthread_key_create(&NAME##_key, free)) { \
+ abort(); \
+ } \
+ } \
+ \
+ static NAME##_type * \
+ NAME##_get(void) \
+ { \
+ static pthread_once_t once = PTHREAD_ONCE_INIT; \
+ NAME##_type *value; \
+ \
+ pthread_once(&once, NAME##_once_init); \
+ value = NAME##_get_unsafe(); \
+ if (!value) { \
+ static const NAME##_type initial_value = __VA_ARGS__; \
+ \
+ value = xmalloc(sizeof *value); \
+ *value = initial_value; \
+ pthread_setspecific(NAME##_key, value); \
+ } \
+ return value; \
+ }
+#endif
+
+/* DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME).
+ *
+ * This is a simple wrapper around POSIX per-thread data primitives. It
+ * defines per-thread variable NAME with the given TYPE, which must be a
+ * pointer type. In each thread, the per-thread variable is initialized to
+ * NULL. When a thread terminates, the variable is freed with free().
+ *
+ * The public interface to the variable is:
+ *
+ * TYPE NAME_get(void)
+ * TYPE NAME_get_unsafe(void)
+ *
+ * Returns the value of per-thread variable NAME in this thread.
+ *
+ * Use NAME_get() in a context where this might be the first use of the
+ * per-thread variable in the program. Use NAME_get_unsafe(), which
+ * avoids a conditional test and is thus slightly faster, in a context
+ * where one knows that NAME_get() has already been called previously.
+ *
+ * TYPE NAME_set(TYPE new_value)
+ * TYPE NAME_set_unsafe(TYPE new_value)
+ *
+ * Sets the value of per-thread variable NAME to 'new_value' in this
+ * thread, and returns its previous value.
+ *
+ * Use NAME_set() in a context where this might be the first use of the
+ * per-thread variable in the program. Use NAME_set_unsafe(), which
+ * avoids a conditional test and is thus slightly faster, in a context
+ * where one knows that NAME_set() has already been called previously.
+ */
+#define DEFINE_PER_THREAD_MALLOCED_DATA(TYPE, NAME) \
+ static pthread_key_t NAME##_key; \
+ \
+ static void \
+ NAME##_once_init(void) \
+ { \
+ if (pthread_key_create(&NAME##_key, free)) { \
+ abort(); \
+ } \
+ } \
+ \
+ static void \
+ NAME##_init(void) \
+ { \
+ static pthread_once_t once = PTHREAD_ONCE_INIT; \
+ pthread_once(&once, NAME##_once_init); \
+ } \
+ \
+ static TYPE \
+ NAME##_get_unsafe(void) \
+ { \
+ return pthread_getspecific(NAME##_key); \
+ } \
+ \
+ static OVS_UNUSED TYPE \
+ NAME##_get(void) \
+ { \
+ NAME##_init(); \
+ return NAME##_get_unsafe(); \
+ } \
+ \
+ static TYPE \
+ NAME##_set_unsafe(TYPE value) \
+ { \
+ TYPE old_value = NAME##_get_unsafe(); \
+ pthread_setspecific(NAME##_key, value); \
+ return old_value; \
+ } \
+ \
+ static OVS_UNUSED TYPE \
+ NAME##_set(TYPE value) \
+ { \
+ NAME##_init(); \
+ return NAME##_set_unsafe(value); \
+ }
+\f
#endif /* ovs-thread.h */
git://git.onelab.eu / sliver-openvswitch.git / blobdiff