+++ /dev/null
-/*
-*******************************************************************************
-* Copyright (C) 2014, International Business Machines Corporation and
-* others. All Rights Reserved.
-*******************************************************************************
-*
-* File SHAREDPTR.H
-*******************************************************************************
-*/
-
-#ifndef __SHARED_PTR_H__
-#define __SHARED_PTR_H__
-
-#include "unicode/uobject.h"
-#include "umutex.h"
-#include "uassert.h"
-
-U_NAMESPACE_BEGIN
-
-// Wrap u_atomic_int32_t in a UMemory so that we allocate them in the same
-// way we allocate all other ICU objects.
-struct AtomicInt : public UMemory {
- u_atomic_int32_t value;
-};
-
-/**
- * SharedPtr are shared pointers that support copy-on-write sematics.
- * SharedPtr makes the act of copying large objects cheap by deferring the
- * cost of the copy to the first write operation after the copy.
- *
- * A SharedPtr<T> instance can refer to no object or an object of type T.
- * T must have a clone() method that copies
- * the object and returns a pointer to the copy. Copy and assignment of
- * SharedPtr instances are cheap because they only involve copying or
- * assigning the SharedPtr instance, not the T object which could be large.
- * Although many SharedPtr<T> instances may refer to the same T object,
- * clients can still assume that each SharedPtr<T> instance has its own
- * private instance of T because each SharedPtr<T> instance offers only a
- * const view of its T object through normal pointer operations. If a caller
- * must change a T object through its SharedPtr<T>, it can do so by calling
- * readWrite() on the SharedPtr instance. readWrite() ensures that the
- * SharedPtr<T> really does have its own private T object by cloning it if
- * it is shared by using its clone() method. SharedPtr<T> instances handle
- * management by reference counting their T objects. T objects that are
- * referenced by no SharedPtr<T> instances get deleted automatically.
- */
-
-// TODO (Travis Keep): Leave interface the same, but find a more efficient
-// implementation that is easier to understand.
-template<typename T>
-class SharedPtr {
-public:
- /**
- * Constructor. If there is a memory allocation error creating
- * reference counter then this object will contain NULL, and adopted
- * pointer will be freed. Note that when passing NULL or no argument to
- * constructor, no memory allocation error can happen as NULL pointers
- * are never reference counted.
- */
- explicit SharedPtr(T *adopted=NULL) : ptr(adopted), refPtr(NULL) {
- if (ptr != NULL) {
- refPtr = new AtomicInt();
- if (refPtr == NULL) {
- delete ptr;
- ptr = NULL;
- } else {
- refPtr->value = 1;
- }
- }
- }
-
- /**
- * Copy constructor.
- */
- SharedPtr(const SharedPtr<T> &other) :
- ptr(other.ptr), refPtr(other.refPtr) {
- if (refPtr != NULL) {
- umtx_atomic_inc(&refPtr->value);
- }
- }
-
- /**
- * assignment operator.
- */
- SharedPtr<T> &operator=(const SharedPtr<T> &other) {
- if (ptr != other.ptr) {
- SharedPtr<T> newValue(other);
- swap(newValue);
- }
- return *this;
- }
-
- /**
- * Destructor.
- */
- ~SharedPtr() {
- if (refPtr != NULL) {
- if (umtx_atomic_dec(&refPtr->value) == 0) {
- delete ptr;
- delete refPtr;
- }
- }
- }
-
- /**
- * reset adopts a new pointer. On success, returns TRUE.
- * On memory allocation error creating reference counter for adopted
- * pointer, returns FALSE while leaving this instance unchanged.
- */
- bool reset(T *adopted) {
- SharedPtr<T> newValue(adopted);
- if (adopted != NULL && newValue.ptr == NULL) {
- // We couldn't allocate ref counter.
- return FALSE;
- }
- swap(newValue);
- return TRUE;
- }
-
- /**
- * reset makes this instance refer to no object.
- */
- void reset() {
- reset(NULL);
- }
-
- /**
- * count returns how many SharedPtr instances, including this one,
- * refer to the T object. Used for testing. Clients need not use in
- * practice.
- */
- int32_t count() const {
- if (refPtr == NULL) {
- return 0;
- }
- return umtx_loadAcquire(refPtr->value);
- }
-
- /**
- * Swaps this instance with other.
- */
- void swap(SharedPtr<T> &other) {
- T *tempPtr = other.ptr;
- AtomicInt *tempRefPtr = other.refPtr;
- other.ptr = ptr;
- other.refPtr = refPtr;
- ptr = tempPtr;
- refPtr = tempRefPtr;
- }
-
- const T *operator->() const {
- return ptr;
- }
-
- const T &operator*() const {
- return *ptr;
- }
-
- bool operator==(const T *other) const {
- return ptr == other;
- }
-
- bool operator!=(const T *other) const {
- return ptr != other;
- }
-
- /**
- * readOnly gives const access to this instance's T object. If this
- * instance refers to no object, returns NULL.
- */
- const T *readOnly() const {
- return ptr;
- }
-
- /**
- * readWrite returns a writable pointer to its T object copying it first
- * using its clone() method if it is shared.
- * On memory allocation error or if this instance refers to no object,
- * this method returns NULL leaving this instance unchanged.
- * <p>
- * If readWrite() returns a non NULL pointer, it guarantees that this
- * object holds the only reference to its T object enabling the caller to
- * perform mutations using the returned pointer without affecting other
- * SharedPtr objects. However, the non-constness of readWrite continues as
- * long as the returned pointer is in scope. Therefore it is an API
- * violation to call readWrite() on A; perform B = A; and then proceed to
- * mutate A via its writeable pointer as that would be the same as setting
- * B = A while A is changing. The returned pointer is guaranteed to be
- * valid only while this object is in scope because this object maintains
- * ownership of its T object. Therefore, callers must never attempt to
- * delete the returned writeable pointer. The best practice with readWrite
- * is this: callers should use the returned pointer from readWrite() only
- * within the same scope as that call to readWrite, and that scope should
- * be made as small as possible avoiding overlap with other operatios on
- * this object.
- */
- T *readWrite() {
- int32_t refCount = count();
- if (refCount <= 1) {
- return ptr;
- }
- T *result = (T *) ptr->clone();
- if (result == NULL) {
- // Memory allocation error
- return NULL;
- }
- if (!reset(result)) {
- return NULL;
- }
- return ptr;
- }
-private:
- T *ptr;
- AtomicInt *refPtr;
- // No heap allocation. Use only stack.
- static void * U_EXPORT2 operator new(size_t size);
- static void * U_EXPORT2 operator new[](size_t size);
-#if U_HAVE_PLACEMENT_NEW
- static void * U_EXPORT2 operator new(size_t, void *ptr);
-#endif
-};
-
-U_NAMESPACE_END
-
-#endif
projects / apple / icu.git / blobdiff