255 lines
11 KiB
C
255 lines
11 KiB
C
/*
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* Copyright (c) 2017 Apple Inc. All rights reserved.
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*
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* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
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*
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* This file contains Original Code and/or Modifications of Original Code
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* as defined in and that are subject to the Apple Public Source License
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* Version 2.0 (the 'License'). You may not use this file except in
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* compliance with the License. The rights granted to you under the License
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* may not be used to create, or enable the creation or redistribution of,
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* unlawful or unlicensed copies of an Apple operating system, or to
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* circumvent, violate, or enable the circumvention or violation of, any
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* terms of an Apple operating system software license agreement.
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*
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* Please obtain a copy of the License at
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* http://www.opensource.apple.com/apsl/ and read it before using this file.
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*
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* The Original Code and all software distributed under the License are
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* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
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* Please see the License for the specific language governing rights and
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* limitations under the License.
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*
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* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
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*/
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#ifndef _OS_REFCNT_H_
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#define _OS_REFCNT_H_
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/*
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* os_refcnt reference counting API
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*
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* Two flavors are provided: atomic and locked. Atomic internally uses C11 atomic
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* operations and requires no external synchronization, whereas the locked flavor
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* assumes the refcnt object is locked by the caller. It is NOT safe to
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* mix-and-match locked and atomic calls.
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*
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* 'refgrp's are a way to (hierarchically) group like refcount objects for
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* debugging purposes. The group keeps track of the total number and aggregate
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* reference count of member refcounts, and the "rlog=" boot-arg is used to enable
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* refcount logging by group name. Named groups can be created explicitly with
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* os_refgrp_decl(), or implicitly by passing NULL for the refgrp when
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* initializing a refcnt object. In the latter case, the group name is the same as
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* the function enclosing the init call. Groups are only available on DEV or DEBUG
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* builds, and are otherwise compiled out.
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*/
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#include <stdatomic.h>
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#include <stdbool.h>
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#include <os/base.h>
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struct os_refcnt;
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struct os_refgrp;
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typedef struct os_refcnt os_refcnt_t;
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/* type of the internal counter */
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typedef uint32_t os_ref_count_t;
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typedef _Atomic(os_ref_count_t) os_ref_atomic_t;
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/*
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* OS_REF_INITIALIZER
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* OS_REF_ATOMIC_INITIALIZER
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*
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* Static initializers that create refcnt objects with safe initial values for use
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* between declaration and initialization (os_ref*_init()). Equivalent to zeroing.
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*/
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#ifndef KERNEL
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# include <stdlib.h>
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# include <stdio.h>
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# ifndef __improbable
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# define __improbable(x) x
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# endif
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# ifndef panic
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# define panic(x, ...) do { fprintf(stderr, x, __VA_ARGS__); abort(); } while (0)
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# endif
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#endif
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#ifndef OS_REFCNT_DEBUG
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# if DEVELOPMENT || DEBUG
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# define OS_REFCNT_DEBUG 1
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# else
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# define OS_REFCNT_DEBUG 0
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# endif
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#endif
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#if __has_attribute(diagnose_if)
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# define os_error_if(cond, msg) __attribute__((diagnose_if((cond), (msg), "error")))
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#else
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# define os_error_if(...)
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#endif
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__BEGIN_DECLS
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/*
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* os_ref_init: initialize an os_refcnt with a count of 1
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* os_ref_init_count: initialize an os_refcnt with a specific count >= 1
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*/
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#define os_ref_init(rc, grp) os_ref_init_count((rc), (grp), 1)
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static void os_ref_init_count(struct os_refcnt *, struct os_refgrp *, os_ref_count_t count)
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os_error_if(count == 0, "Reference count must be non-zero initialized");
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/*
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* os_refgrp_decl(qual, var, name, parent): declare a refgroup object 'var' with
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* given name string and parent group.
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*/
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/*
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*
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* os_ref_retain: acquire a reference (increment reference count by 1) atomically.
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*
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* os_ref_release: release a reference (decrement reference count) atomically and
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* return the new count. Memory is synchronized such that the dealloc block
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* (i.e. code handling the final release() == 0 call) sees up-to-date memory
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* with respect to all prior release()s on the same refcnt object. This
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* memory ordering is sufficient for most use cases.
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*
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* os_ref_release_relaxed: same as release() but with weaker relaxed memory ordering.
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* This can be used when the dealloc block is already synchronized with other
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* accesses to the object (for example, with a lock).
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*
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* os_ref_release_live: release a reference that is guaranteed not to be the last one.
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*/
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static void os_ref_retain(struct os_refcnt *);
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static os_ref_count_t os_ref_release(struct os_refcnt *) OS_WARN_RESULT;
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static os_ref_count_t os_ref_release_relaxed(struct os_refcnt *) OS_WARN_RESULT;
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static void os_ref_release_live(struct os_refcnt *);
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/*
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* os_ref_retain_try: a variant of atomic retain that fails for objects with a
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* zero reference count. The caller must therefore ensure that the object
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* remains alive for any possible retain_try() caller, usually by using a
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* lock protecting both the retain and dealloc paths. This variant is useful
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* for objects stored in a collection, because no lock is required on the
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* release() side until the object is deallocated.
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*/
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static bool os_ref_retain_try(struct os_refcnt *) OS_WARN_RESULT;
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/*
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* os_ref_retain_locked: acquire a reference on an object protected by a held
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* lock. The caller must ensure mutual exclusivity of retain_locked() and
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* release_locked() calls on the same object.
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*
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* os_ref_release_locked: release a reference on an object protected by a held
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* lock.
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*/
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static void os_ref_retain_locked(struct os_refcnt *);
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static os_ref_count_t os_ref_release_locked(struct os_refcnt *) OS_WARN_RESULT;
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/*
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* os_ref_get_count: return the current reference count. This is unsafe for
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* synchronization.
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*/
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static os_ref_count_t os_ref_get_count(struct os_refcnt *rc);
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#if XNU_KERNEL_PRIVATE
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#pragma GCC visibility push(hidden)
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/*
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* Raw API that uses a plain atomic counter (os_ref_atomic_t) and a separate
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* refgroup. This can be used in situations where the refcount object must be
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* fixed size, for example for embedding in structures with ABI stability
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* requirements.
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*/
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#define os_ref_init_raw(rc, grp) os_ref_init_count_raw((rc), (grp), 1)
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static void os_ref_init_count_raw(os_ref_atomic_t *, struct os_refgrp *, os_ref_count_t count)
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os_error_if(count == 0, "Reference count must be non-zero initialized");
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static void os_ref_retain_floor(struct os_refcnt *, os_ref_count_t f)
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os_error_if(!__builtin_constant_p(f) || f == 0, "refcount floor must be >= 1");
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static void os_ref_retain_raw(os_ref_atomic_t *, struct os_refgrp *);
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static void os_ref_retain_floor_raw(os_ref_atomic_t *, os_ref_count_t f, struct os_refgrp *)
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os_error_if(!__builtin_constant_p(f) || f == 0, "refcount floor must be >= 1");
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static os_ref_count_t os_ref_release_raw(os_ref_atomic_t *, struct os_refgrp *) OS_WARN_RESULT;
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static os_ref_count_t os_ref_release_raw_relaxed(os_ref_atomic_t *, struct os_refgrp *) OS_WARN_RESULT;
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static void os_ref_release_live_raw(os_ref_atomic_t *, struct os_refgrp *);
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static bool os_ref_retain_try_raw(os_ref_atomic_t *, struct os_refgrp *) OS_WARN_RESULT;
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static bool os_ref_retain_floor_try_raw(os_ref_atomic_t *, os_ref_count_t f, struct os_refgrp *) OS_WARN_RESULT
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os_error_if(!__builtin_constant_p(f) || f == 0, "refcount floor must be >= 1");
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static void os_ref_retain_locked_raw(os_ref_atomic_t *, struct os_refgrp *);
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static void os_ref_retain_floor_locked_raw(os_ref_atomic_t *, os_ref_count_t f, struct os_refgrp *)
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os_error_if(!__builtin_constant_p(f) || f == 0, "refcount floor must be >= 1");
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static os_ref_count_t os_ref_release_locked_raw(os_ref_atomic_t *, struct os_refgrp *) OS_WARN_RESULT;
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static os_ref_count_t os_ref_get_count_raw(os_ref_atomic_t *rc);
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/*
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* Bitwise API: like the raw API, but allows some bits in the refcount value to be
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* reserved for other purposes. 'b' defines the number of trailing (LSB) reserved
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* bits, which the refcnt_raw API will never modify (except at init()).
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*
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* It is assumed that users of this API always use atomic ops on the
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* os_ref_atomic_t (or hold a lock for the locked variants), and never modify the
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* top (32 - 'b') bits.
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*
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* Due to guard bits, the maximum reference count is 2^(28 - 'b') - 1, and the
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* maximum 'b' is 26 bits. This API can also be used just to limit the max
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* refcount.
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*
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* The "*_raw_mask" APIs return the raw bit pattern of the refcount (with a type
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* of uint32_t), that the caller is supposed to decode. Other APIs that return
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* os_ref_count_t return a normalized refcount where the trailing bits have been
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* removed.
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*
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* "locked" variants aren't provided as the point of these interfaces
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* is to combine flags into a refcount and be able to manipulate both
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* atomically with respect to each other.
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*/
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/* Initialize the reference count and reserved bits */
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#define os_ref_init_mask(rc, b, grp, bits) os_ref_init_count_mask((rc), (b), (grp), 1, bits)
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void os_ref_init_count_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp,
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os_ref_count_t init_count, uint32_t init_bits)
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os_error_if(init_count == 0, "Reference count must be non-zero initialized")
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os_error_if(b > 26, "Bitwise reference count limited to 26 bits")
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os_error_if(init_bits >= (1U << b), "Bits out of range");
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static uint32_t os_ref_get_raw_mask(os_ref_atomic_t *rc);
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static uint32_t os_ref_get_bits_mask(os_ref_atomic_t *rc, uint32_t b);
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static os_ref_count_t os_ref_get_count_mask(os_ref_atomic_t *rc, uint32_t b);
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static void
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os_ref_retain_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp);
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static void
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os_ref_retain_acquire_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp);
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static uint32_t
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os_ref_retain_try_mask(os_ref_atomic_t *, uint32_t b, uint32_t reject_mask,
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struct os_refgrp *grp) OS_WARN_RESULT;
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static bool
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os_ref_retain_try_acquire_mask(os_ref_atomic_t *, uint32_t b, uint32_t reject_mask,
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struct os_refgrp *grp) OS_WARN_RESULT;
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static uint32_t
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os_ref_release_raw_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp) OS_WARN_RESULT;
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static uint32_t
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os_ref_release_raw_relaxed_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp) OS_WARN_RESULT;
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static os_ref_count_t
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os_ref_release_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp) OS_WARN_RESULT;
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static os_ref_count_t
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os_ref_release_relaxed_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp) OS_WARN_RESULT;
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static uint32_t
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os_ref_release_live_raw_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp);
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static void
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os_ref_release_live_mask(os_ref_atomic_t *rc, uint32_t b, struct os_refgrp *grp);
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#pragma GCC visibility pop
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#endif /* XNU_KERNEL_PRIVATE */
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__END_DECLS
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#include <os/refcnt_internal.h>
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#endif
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