/*
- * Copyright (c) 2013 Nicira, Inc.
+ * Copyright (c) 2013, 2014 Nicira, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#endif
void xpthread_key_create(pthread_key_t *, void (*destructor)(void *));
+void xpthread_key_delete(pthread_key_t);
void xpthread_setspecific(pthread_key_t, const 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:
+ *
+ * Standard Forms
+ * ==============
+ *
+ * Multiple forms of standard per-thread data exist, each with its own pluses
+ * and minuses. In general, if one of these forms is appropriate, then it's a
+ * good idea to use it:
*
* - 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.
+ * pthread_key_t value. It is relatively slow. Typically few
+ * "pthread_key_t"s are available (POSIX requires only at least 128,
+ * glibc supplies only 1024).
*
* - 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
* 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.
+ * ends. Typical implementations allow for an arbitrary amount of
+ * thread_local storage, but statically allocated only.
*
* - The __thread keyword is a GCC extension similar to thread_local but
* with a longer history. __thread is not portable to every GCC version
* needs key allocation? yes no no
* arbitrary initializer? no yes yes
* cross-thread access? yes no yes
+ * amount available? few arbitrary arbitrary
+ * dynamically allocated? yes no no
+ *
+ *
+ * Extensions
+ * ==========
+ *
+ * OVS provides some extensions and wrappers:
+ *
+ * - In a situation where the performance of thread_local or __thread is
+ * desirable, but portability is required, DEFINE_STATIC_PER_THREAD_DATA
+ * and DECLARE_EXTERN_PER_THREAD_DATA/DEFINE_EXTERN_PER_THREAD_DATA may
+ * be appropriate (see below).
+ *
+ * - DEFINE_PER_THREAD_MALLOCED_DATA can be convenient for simple
+ * per-thread malloc()'d buffers.
+ *
+ * - struct ovs_tsd provides an alternative to pthread_key_t that isn't
+ * limited to a small number of keys.
*/
/* For static data, use this macro in a source file:
if (!value) { \
static const NAME##_type initial_value = __VA_ARGS__; \
\
- value = xmalloc(sizeof *value); \
+ value = malloc(sizeof *value); \
+ if (value == NULL) { \
+ out_of_memory(); \
+ } \
*value = initial_value; \
xpthread_setspecific(NAME##_key, value); \
} \
if (!value) { \
static const NAME##_type initial_value = __VA_ARGS__; \
\
- value = xmalloc(sizeof *value); \
+ value = malloc(sizeof *value); \
+ if (value == NULL) { \
+ out_of_memory(); \
+ } \
*value = initial_value; \
xpthread_setspecific(NAME##_key, value); \
} \
NAME##_init(); \
return NAME##_set_unsafe(value); \
}
+
+/* Dynamically allocated thread-specific data with lots of slots.
+ *
+ * pthread_key_t can provide as few as 128 pieces of thread-specific data (even
+ * glibc is limited to 1,024). Thus, one must be careful to allocate only a
+ * few keys globally. One cannot, for example, allocate a key for every
+ * instance of a data structure if there might be an arbitrary number of those
+ * data structures.
+ *
+ * This API is similar to the pthread one (simply search and replace pthread_
+ * by ovsthread_) but it a much larger limit that can be raised if necessary
+ * (by recompiling). Thus, one may more freely use this form of
+ * thread-specific data.
+ *
+ * Compared to pthread_key_t, ovsthread_key_t has the follow limitations:
+ *
+ * - Destructors must not access thread-specific data (via ovsthread_key).
+ */
+typedef struct ovsthread_key *ovsthread_key_t;
+
+void ovsthread_key_create(ovsthread_key_t *, void (*destructor)(void *));
+void ovsthread_key_delete(ovsthread_key_t);
+
+void ovsthread_setspecific(ovsthread_key_t, const void *);
+void *ovsthread_getspecific(ovsthread_key_t);
\f
/* Convenient once-only execution.
*
OVS_TRY_LOCK(false, once->mutex);
static inline bool
-ovsthread_once_is_done__(const struct ovsthread_once *once)
+ovsthread_once_is_done__(struct ovsthread_once *once)
{
bool done;
void forbid_forking(const char *reason);
bool may_fork(void);
+\f
+/* Useful functions related to threading. */
+
+int count_cpu_cores(void);
#endif /* ovs-thread.h */
projects / cascardo / ovs.git / blobdiff