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      1 /*
      2  * Copyright (C) 2018 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef SRC_TRACE_PROCESSOR_TRACE_BLOB_VIEW_H_
     18 #define SRC_TRACE_PROCESSOR_TRACE_BLOB_VIEW_H_
     19 
     20 #include <stddef.h>
     21 #include <stdint.h>
     22 
     23 #include <limits>
     24 #include <memory>
     25 
     26 #include "perfetto/base/logging.h"
     27 
     28 namespace perfetto {
     29 namespace trace_processor {
     30 
     31 // This class is an equivalent of std::string_view for trace binary data.
     32 // The main difference is that this class has also shared ownership of a portion
     33 // of the raw trace.
     34 // The underlying buffer will be freed once all the TraceBlobViews that refer
     35 // to the same buffer have passed through the pipeline and been parsed.
     36 class TraceBlobView {
     37  public:
     38   TraceBlobView(std::unique_ptr<uint8_t[]> buffer, size_t offset, size_t length)
     39       : shbuf_(SharedBuf(std::move(buffer))),
     40         offset_(static_cast<uint32_t>(offset)),
     41         length_(static_cast<uint32_t>(length)) {
     42     PERFETTO_DCHECK(offset <= std::numeric_limits<uint32_t>::max());
     43     PERFETTO_DCHECK(length <= std::numeric_limits<uint32_t>::max());
     44   }
     45 
     46   // Allow std::move().
     47   TraceBlobView(TraceBlobView&&) noexcept = default;
     48   TraceBlobView& operator=(TraceBlobView&&) = default;
     49 
     50   // Disable implicit copy.
     51   TraceBlobView(const TraceBlobView&) = delete;
     52   TraceBlobView& operator=(const TraceBlobView&) = delete;
     53 
     54   TraceBlobView slice(size_t offset, size_t length) {
     55     PERFETTO_DCHECK(offset + length <= offset_ + length_);
     56     return TraceBlobView(shbuf_, offset, length);
     57   }
     58 
     59   bool operator==(const TraceBlobView& rhs) const {
     60     return (shbuf_ == rhs.shbuf_) && (offset_ == rhs.offset_) &&
     61            (length_ == rhs.length_);
     62   }
     63   bool operator!=(const TraceBlobView& rhs) const { return !(*this == rhs); }
     64 
     65   inline const uint8_t* data() const { return start() + offset_; }
     66 
     67   size_t offset_of(const uint8_t* data) const {
     68     // When a field is size 0, data can be equal to start() + offset_ + length_.
     69     PERFETTO_DCHECK(data >= start() && data <= (start() + offset_ + length_));
     70     return static_cast<size_t>(data - start());
     71   }
     72 
     73   size_t length() const { return length_; }
     74   size_t offset() const { return offset_; }
     75 
     76  private:
     77   // An equivalent to std::shared_ptr<uint8_t>, with the differnce that:
     78   // - Supports array types, available for shared_ptr only in C++17.
     79   // - Is not thread safe, which is not needed for our purposes.
     80   class SharedBuf {
     81    public:
     82     explicit SharedBuf(std::unique_ptr<uint8_t[]> mem) {
     83       rcbuf_ = new RefCountedBuf(std::move(mem));
     84     }
     85 
     86     SharedBuf(const SharedBuf& copy) : rcbuf_(copy.rcbuf_) {
     87       PERFETTO_DCHECK(rcbuf_->refcount > 0);
     88       rcbuf_->refcount++;
     89     }
     90 
     91     ~SharedBuf() {
     92       if (!rcbuf_)
     93         return;
     94       PERFETTO_DCHECK(rcbuf_->refcount > 0);
     95       if (--rcbuf_->refcount == 0) {
     96         RefCountedBuf* rcbuf = rcbuf_;
     97         rcbuf_ = nullptr;
     98         delete rcbuf;
     99       }
    100     }
    101 
    102     SharedBuf(SharedBuf&& other) noexcept {
    103       rcbuf_ = other.rcbuf_;
    104       other.rcbuf_ = nullptr;
    105     }
    106 
    107     SharedBuf& operator=(SharedBuf&& other) {
    108       if (this != &other) {
    109         // A bit of a ugly but pragmatic pattern to implement move assignment.
    110         // First invoke the distructor and then invoke the move constructor
    111         // inline via placement-new.
    112         this->~SharedBuf();
    113         new (this) SharedBuf(std::move(other));
    114       }
    115       return *this;
    116     }
    117 
    118     bool operator==(const SharedBuf& x) const { return x.rcbuf_ == rcbuf_; }
    119     bool operator!=(const SharedBuf& x) const { return !(x == *this); }
    120     const uint8_t* data() const { return rcbuf_->mem.get(); }
    121 
    122    private:
    123     struct RefCountedBuf {
    124       explicit RefCountedBuf(std::unique_ptr<uint8_t[]> buf)
    125           : refcount(1), mem(std::move(buf)) {}
    126       int refcount;
    127       std::unique_ptr<uint8_t[]> mem;
    128     };
    129 
    130     RefCountedBuf* rcbuf_ = nullptr;
    131   };
    132 
    133   inline const uint8_t* start() const { return shbuf_.data(); }
    134 
    135   TraceBlobView(SharedBuf b, size_t o, size_t l)
    136       : shbuf_(b),
    137         offset_(static_cast<uint32_t>(o)),
    138         length_(static_cast<uint32_t>(l)) {}
    139 
    140   SharedBuf shbuf_;
    141   uint32_t offset_;
    142   uint32_t length_;  // Measured from |offset_|, not from |data()|.
    143 };
    144 
    145 }  // namespace trace_processor
    146 }  // namespace perfetto
    147 
    148 #endif  // SRC_TRACE_PROCESSOR_TRACE_BLOB_VIEW_H_
    149