/*
- * Copyright (c) 2014 Nicira, Inc.
+ * Copyright (c) 2014, 2015, 2016 Nicira, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* A "quiescent state" is a time at which a thread holds no pointers to memory
* that is managed by RCU; that is, when the thread is known not to reference
* memory that might be an old version of some object freed via RCU. For
- * example, poll_block() includes a quiescent state, as does
- * ovs_mutex_cond_wait().
+ * example, poll_block() includes a quiescent state.
*
* The following functions manage the recognition of quiescent states:
*
*
* Brackets a time period during which the current thread is quiescent.
*
- * A newly created thread is initially active, not quiescent.
+ * A newly created thread is initially active, not quiescent. When a process
+ * becomes multithreaded, the main thread becomes active, not quiescent.
*
* When a quiescient state has occurred in every thread, we say that a "grace
* period" has occurred. Following a grace period, all of the callbacks
- * postponed before the start of the grace period may be invoked. OVS takes
+ * postponed before the start of the grace period MAY be invoked. OVS takes
* care of this automatically through the RCU mechanism: while a process still
* has only a single thread, it invokes the postponed callbacks directly from
* ovsrcu_quiesce() and ovsrcu_quiesce_start(); after additional threads have
* been created, it creates an extra helper thread to invoke callbacks.
*
+ * Please note that while a postponed function call is guaranteed to happen
+ * after the next time all participating threads have quiesced at least once,
+ * there is no quarantee that all postponed functions are called as early as
+ * possible, or that the functions postponed by different threads would be
+ * called in the order the registrations took place. In particular, even if
+ * two threads provably postpone a function each in a specific order, the
+ * postponed functions may still be called in the opposite order, depending on
+ * the timing of when the threads call ovsrcu_quiesce(), how many functions
+ * they postpone, and when the ovs-rcu thread happens to grab the functions to
+ * be called.
*
- * Use
- * ---
+ * All functions postponed by a single thread are guaranteed to execute in the
+ * order they were postponed, however.
+ *
+ * Usage
+ * -----
*
* Use OVSRCU_TYPE(TYPE) to declare a pointer to RCU-protected data, e.g. the
* following declares an RCU-protected "struct flow *" named flowp:
* compilers will merrily carry along accepting the wrong type.)
*
* Use ovsrcu_set() to write an RCU-protected pointer and ovsrcu_postpone() to
- * free the previous data. ovsrcu_init() can be used on (newly created) RCU-
- * protected pointer that is not yet visible to the readers. If more than one
- * thread can write the pointer, then some form of external synchronization,
- * e.g. a mutex, is needed to prevent writers from interfering with one
- * another. For example, to write the pointer variable declared above while
- * safely freeing the old value:
+ * free the previous data. ovsrcu_set_hidden() can be used on RCU protected
+ * data not visible to any readers yet, but will be made visible by a later
+ * ovsrcu_set(). ovsrcu_init() can be used to initialize RCU pointers when
+ * no readers are yet executing. If more than one thread can write the
+ * pointer, then some form of external synchronization, e.g. a mutex, is
+ * needed to prevent writers from interfering with one another. For example,
+ * to write the pointer variable declared above while safely freeing the old
+ * value:
*
* static struct ovs_mutex mutex = OVS_MUTEX_INITIALIZER;
*
#if __GNUC__
#define OVSRCU_TYPE(TYPE) struct { ATOMIC(TYPE) p; }
-#define OVSRCU_TYPE_INITIALIZER { NULL }
+#define OVSRCU_INITIALIZER(VALUE) { ATOMIC_VAR_INIT(VALUE) }
#define ovsrcu_get__(TYPE, VAR, ORDER) \
({ \
TYPE value__; \
+ typeof(VAR) ovsrcu_var = (VAR); \
\
- atomic_read_explicit(CONST_CAST(ATOMIC(TYPE) *, &(VAR)->p), \
+ atomic_read_explicit(CONST_CAST(ATOMIC(TYPE) *, &ovsrcu_var->p), \
&value__, ORDER); \
\
value__; \
})
#define ovsrcu_get(TYPE, VAR) \
- CONST_CAST(TYPE, ovsrcu_get__(TYPE, VAR, memory_order_consume))
+ ovsrcu_get__(TYPE, VAR, memory_order_consume)
#define ovsrcu_get_protected(TYPE, VAR) \
- CONST_CAST(TYPE, ovsrcu_get__(TYPE, VAR, memory_order_relaxed))
+ ovsrcu_get__(TYPE, VAR, memory_order_relaxed)
+
+/* 'VALUE' may be an atomic operation, which must be evaluated before
+ * any of the body of the atomic_store_explicit. Since the type of
+ * 'VAR' is not fixed, we cannot use an inline function to get
+ * function semantics for this. */
+#define ovsrcu_set__(VAR, VALUE, ORDER) \
+ ({ \
+ typeof(VAR) ovsrcu_var = (VAR); \
+ typeof(VALUE) ovsrcu_value = (VALUE); \
+ memory_order ovsrcu_order = (ORDER); \
+ \
+ atomic_store_explicit(&ovsrcu_var->p, ovsrcu_value, ovsrcu_order); \
+ (void *) 0; \
+ })
#else /* not GNU C */
-typedef struct ovsrcu_pointer { ATOMIC(void *) p; };
+struct ovsrcu_pointer { ATOMIC(void *) p; };
#define OVSRCU_TYPE(TYPE) struct ovsrcu_pointer
-#define OVSRCU_TYPE_INITIALIZER { NULL }
+#define OVSRCU_INITIALIZER(VALUE) { ATOMIC_VAR_INIT(VALUE) }
static inline void *
ovsrcu_get__(const struct ovsrcu_pointer *pointer, memory_order order)
{
CONST_CAST(TYPE, ovsrcu_get__(VAR, memory_order_consume))
#define ovsrcu_get_protected(TYPE, VAR) \
CONST_CAST(TYPE, ovsrcu_get__(VAR, memory_order_relaxed))
+
+static inline void ovsrcu_set__(struct ovsrcu_pointer *pointer,
+ const void *value,
+ memory_order order)
+{
+ atomic_store_explicit(&pointer->p, CONST_CAST(void *, value), order);
+}
#endif
/* Writes VALUE to the RCU-protected pointer whose address is VAR.
* Users require external synchronization (e.g. a mutex). See "Usage" above
* for an example. */
#define ovsrcu_set(VAR, VALUE) \
- atomic_store_explicit(&(VAR)->p, VALUE, memory_order_release)
+ ovsrcu_set__(VAR, VALUE, memory_order_release)
/* This can be used for initializing RCU pointers before any readers can
* see them. A later ovsrcu_set() needs to make the bigger structure this
* is part of visible to the readers. */
-#define ovsrcu_init(VAR, VALUE) \
- atomic_store_explicit(&(VAR)->p, VALUE, memory_order_relaxed)
+#define ovsrcu_set_hidden(VAR, VALUE) \
+ ovsrcu_set__(VAR, VALUE, memory_order_relaxed)
+
+/* This can be used for initializing RCU pointers before any readers are
+ * executing. */
+#define ovsrcu_init(VAR, VALUE) atomic_init(&(VAR)->p, VALUE)
/* Calls FUNCTION passing ARG as its pointer-type argument following the next
- * grace period. See "Usage" above for example. */
+ * grace period. See "Usage" above for an example. */
void ovsrcu_postpone__(void (*function)(void *aux), void *aux);
#define ovsrcu_postpone(FUNCTION, ARG) \
- ((void) sizeof((FUNCTION)(ARG), 1), \
+ (/* Verify that ARG is appropriate for FUNCTION. */ \
+ (void) sizeof((FUNCTION)(ARG), 1), \
+ /* Verify that ARG is a pointer type. */ \
(void) sizeof(*(ARG)), \
ovsrcu_postpone__((void (*)(void *))(FUNCTION), ARG))
void ovsrcu_quiesce(void);
bool ovsrcu_is_quiescent(void);
+/* Synchronization. Waits for all non-quiescent threads to quiesce at least
+ * once. This can block for a relatively long time. */
+void ovsrcu_synchronize(void);
+
#endif /* ovs-rcu.h */
projects / cascardo / ovs.git / blobdiff