summaryrefslogtreecommitdiffstats
blob: 7910c6e0ee5c9ccde408656fb9c98142f53d24af (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
/*
 * Copyright (C) 2005 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "sharedbuffer"

#include "SharedBuffer.h"

#include <stdlib.h>
#include <string.h>

#include <log/log.h>

// ---------------------------------------------------------------------------

namespace android {

SharedBuffer* SharedBuffer::alloc(size_t size)
{
    // Don't overflow if the combined size of the buffer / header is larger than
    // size_max.
    LOG_ALWAYS_FATAL_IF((size >= (SIZE_MAX - sizeof(SharedBuffer))),
                        "Invalid buffer size %zu", size);

    SharedBuffer* sb = static_cast<SharedBuffer *>(malloc(sizeof(SharedBuffer) + size));
    if (sb) {
        // Should be std::atomic_init(&sb->mRefs, 1);
        // But that generates a warning with some compilers.
        // The following is OK on Android-supported platforms.
        sb->mRefs.store(1, std::memory_order_relaxed);
        sb->mSize = size;
    }
    return sb;
}


void SharedBuffer::dealloc(const SharedBuffer* released)
{
    free(const_cast<SharedBuffer*>(released));
}

SharedBuffer* SharedBuffer::edit() const
{
    if (onlyOwner()) {
        return const_cast<SharedBuffer*>(this);
    }
    SharedBuffer* sb = alloc(mSize);
    if (sb) {
        memcpy(sb->data(), data(), size());
        release();
    }
    return sb;
}

SharedBuffer* SharedBuffer::editResize(size_t newSize) const
{
    if (onlyOwner()) {
        SharedBuffer* buf = const_cast<SharedBuffer*>(this);
        if (buf->mSize == newSize) return buf;
        // Don't overflow if the combined size of the new buffer / header is larger than
        // size_max.
        LOG_ALWAYS_FATAL_IF((newSize >= (SIZE_MAX - sizeof(SharedBuffer))),
                            "Invalid buffer size %zu", newSize);

        buf = (SharedBuffer*)realloc(buf, sizeof(SharedBuffer) + newSize);
        if (buf != nullptr) {
            buf->mSize = newSize;
            return buf;
        }
    }
    SharedBuffer* sb = alloc(newSize);
    if (sb) {
        const size_t mySize = mSize;
        memcpy(sb->data(), data(), newSize < mySize ? newSize : mySize);
        release();
    }
    return sb;    
}

SharedBuffer* SharedBuffer::attemptEdit() const
{
    if (onlyOwner()) {
        return const_cast<SharedBuffer*>(this);
    }
    return nullptr;
}

SharedBuffer* SharedBuffer::reset(size_t new_size) const
{
    // cheap-o-reset.
    SharedBuffer* sb = alloc(new_size);
    if (sb) {
        release();
    }
    return sb;
}

void SharedBuffer::acquire() const {
    mRefs.fetch_add(1, std::memory_order_relaxed);
}

int32_t SharedBuffer::release(uint32_t flags) const
{
    const bool useDealloc = ((flags & eKeepStorage) == 0);
    if (onlyOwner()) {
        // Since we're the only owner, our reference count goes to zero.
        mRefs.store(0, std::memory_order_relaxed);
        if (useDealloc) {
            dealloc(this);
        }
        // As the only owner, our previous reference count was 1.
        return 1;
    }
    // There's multiple owners, we need to use an atomic decrement.
    int32_t prevRefCount = mRefs.fetch_sub(1, std::memory_order_release);
    if (prevRefCount == 1) {
        // We're the last reference, we need the acquire fence.
        atomic_thread_fence(std::memory_order_acquire);
        if (useDealloc) {
            dealloc(this);
        }
    }
    return prevRefCount;
}


}; // namespace android