From: Mathieu Desnoyers Date: Mon, 11 May 2009 02:20:47 +0000 (-0400) Subject: Add missing urcu-static.h X-Git-Tag: v0.1~242 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=adcfce542ec1c28796c3c641021a6d37f97b6f6f;p=urcu.git Add missing urcu-static.h This new file should be inly included in LGPL-compatible code. Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-static.h b/urcu-static.h new file mode 100644 index 0000000..c47a759 --- /dev/null +++ b/urcu-static.h @@ -0,0 +1,277 @@ +#ifndef _URCU_STATIC_H +#define _URCU_STATIC_H + +/* + * urcu-static.h + * + * Userspace RCU header, to be included only in LGPL-compatible code. + * + * Copyright February 2009 - Mathieu Desnoyers + * + * Credits for Paul E. McKenney + * for inspiration coming from the Linux kernel RCU and rcu-preempt. + * + * Distributed under LGPLv2.1 + * + * IBM's contributions to this file may be relicensed under LGPLv2 or later. + */ + +#include +#include + +#include +#include + +/* + * Identify a shared load. A smp_rmc() or smp_mc() should come before the load. + */ +#define _LOAD_SHARED(p) ACCESS_ONCE(p) + +/* + * Load a data from shared memory, doing a cache flush if required. + */ +#define LOAD_SHARED(p) \ + ({ \ + smp_rmc(); \ + _LOAD_SHARED(p); \ + }) + +/* + * Identify a shared store. A smp_wmc() or smp_mc() should follow the store. + */ +#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); }) + +/* + * Store v into x, where x is located in shared memory. Performs the required + * cache flush after writing. Returns v. + */ +#define STORE_SHARED(x, v) \ + ({ \ + _STORE_SHARED(x, v); \ + smp_wmc(); \ + (v); \ + }) + +/** + * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable + * into a RCU read-side critical section. The pointer can later be safely + * dereferenced within the critical section. + * + * This ensures that the pointer copy is invariant thorough the whole critical + * section. + * + * Inserts memory barriers on architectures that require them (currently only + * Alpha) and documents which pointers are protected by RCU. + * + * Should match rcu_assign_pointer() or rcu_xchg_pointer(). + */ + +#define _rcu_dereference(p) ({ \ + typeof(p) _________p1 = LOAD_SHARED(p); \ + smp_read_barrier_depends(); \ + (_________p1); \ + }) + +/* + * This code section can only be included in LGPL 2.1 compatible source code. + * See below for the function call wrappers which can be used in code meant to + * be only linked with the Userspace RCU library. This comes with a small + * performance degradation on the read-side due to the added function calls. + * This is required to permit relinking with newer versions of the library. + */ + +/* + * The signal number used by the RCU library can be overridden with + * -DSIGURCU= when compiling the library. + */ +#ifndef SIGURCU +#define SIGURCU SIGUSR1 +#endif + +/* + * If a reader is really non-cooperative and refuses to commit its + * urcu_active_readers count to memory (there is no barrier in the reader + * per-se), kick it after a few loops waiting for it. + */ +#define KICK_READER_LOOPS 10000 + +#ifdef DEBUG_YIELD +#include +#include +#include +#include + +#define YIELD_READ (1 << 0) +#define YIELD_WRITE (1 << 1) + +/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */ +#ifdef DEBUG_FULL_MB +/* maximum sleep delay, in us */ +#define MAX_SLEEP 50 +#else +#define MAX_SLEEP 30000 +#endif + +extern unsigned int yield_active; +extern unsigned int __thread rand_yield; + +static inline void debug_yield_read(void) +{ + if (yield_active & YIELD_READ) + if (rand_r(&rand_yield) & 0x1) + usleep(rand_r(&rand_yield) % MAX_SLEEP); +} + +static inline void debug_yield_write(void) +{ + if (yield_active & YIELD_WRITE) + if (rand_r(&rand_yield) & 0x1) + usleep(rand_r(&rand_yield) % MAX_SLEEP); +} + +static inline void debug_yield_init(void) +{ + rand_yield = time(NULL) ^ pthread_self(); +} +#else +static inline void debug_yield_read(void) +{ +} + +static inline void debug_yield_write(void) +{ +} + +static inline void debug_yield_init(void) +{ + +} +#endif + +#ifdef DEBUG_FULL_MB +static inline void reader_barrier() +{ + smp_mb(); +} +#else +static inline void reader_barrier() +{ + barrier(); +} +#endif + +/* + * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a + * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits. + */ +#define RCU_GP_COUNT (1UL << 0) +/* Use the amount of bits equal to half of the architecture long size */ +#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2)) +#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1) + +/* + * Global quiescent period counter with low-order bits unused. + * Using a int rather than a char to eliminate false register dependencies + * causing stalls on some architectures. + */ +extern long urcu_gp_ctr; + +extern long __thread urcu_active_readers; + +static inline int rcu_old_gp_ongoing(long *value) +{ + long v; + + if (value == NULL) + return 0; + /* + * Make sure both tests below are done on the same version of *value + * to insure consistency. + */ + v = LOAD_SHARED(*value); + return (v & RCU_GP_CTR_NEST_MASK) && + ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT); +} + +static inline void _rcu_read_lock(void) +{ + long tmp; + + tmp = urcu_active_readers; + /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */ + /* + * The data dependency "read urcu_gp_ctr, write urcu_active_readers", + * serializes those two memory operations. The memory barrier in the + * signal handler ensures we receive the proper memory commit barriers + * required by _STORE_SHARED and _LOAD_SHARED whenever communication + * with the writer is needed. + */ + if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) + _STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr)); + else + _STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT); + /* + * Increment active readers count before accessing the pointer. + * See force_mb_all_threads(). + */ + reader_barrier(); +} + +static inline void _rcu_read_unlock(void) +{ + reader_barrier(); + /* + * Finish using rcu before decrementing the pointer. + * See force_mb_all_threads(). + */ + _STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT); +} + +/** + * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure + * meant to be read by RCU read-side critical sections. Returns the assigned + * value. + * + * Documents which pointers will be dereferenced by RCU read-side critical + * sections and adds the required memory barriers on architectures requiring + * them. It also makes sure the compiler does not reorder code initializing the + * data structure before its publication. + * + * Should match rcu_dereference_pointer(). + */ + +#define _rcu_assign_pointer(p, v) \ + ({ \ + if (!__builtin_constant_p(v) || \ + ((v) != NULL)) \ + wmb(); \ + STORE_SHARED(p, v); \ + }) + +/** + * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous + * pointer to the data structure, which can be safely freed after waitin for a + * quiescent state using synchronize_rcu(). + */ + +#define _rcu_xchg_pointer(p, v) \ + ({ \ + if (!__builtin_constant_p(v) || \ + ((v) != NULL)) \ + wmb(); \ + xchg(p, v); \ + }) + +/* + * Exchanges the pointer and waits for quiescent state. + * The pointer returned can be freed. + */ +#define _rcu_publish_content(p, v) \ + ({ \ + void *oldptr; \ + oldptr = _rcu_xchg_pointer(p, v); \ + synchronize_rcu(); \ + oldptr; \ + }) + +#endif /* _URCU_STATIC_H */