我的一些用户报告了崩溃。我不确定我的想法是否正确，所以我展示了代码和崩溃报告的错误描述部分，也许有人对我有帮助的提示。
用例: Assets 目录中的一个文件包含多个国家边界线的坐标。里面还有一些字符串。此代码片段读取文件并将转换后的数据存储到变量中。
有时应用程序会在代码片段的最后一行崩溃(我每周收到 1 或 2 次报告)(let numberOfCountries = Int(dataReadBufferUInt64))。我有一组 Beta 测试人员，他们完全没有问题。所以这是一个令人沮丧的问题。
我认为这与我如何从文件中读取数据有关。也许我必须使用其他方式？
欢迎任何帮助/评论!
数据结构:
Assets 是以编程方式生成的文件。代码片段正在处理此文件的 header 。
第一个元素是版权字符串，其中包含文件版本、创建日期等一些信息。
字符串有两个元素: 1) 作为 UInt16 值的字符串长度(范围 0 ... UInt16.max) 2) 字符串元素(如果长度 > 0)，每个“字符”作为一个 UInt16 值
第二个元素是该文件中的国家/地区数量。这是一个 UInt64 值。
其余的数据结构相当复杂，但在这里不相关，因为文件是顺序读取的，如果它崩溃，它会在读取/转换 UInt64 时崩溃。
“out in the wild”文件只有一个版本。每次用户界面建立时，每个应用程序都会读取此文件。这就是为什么我不明白偶尔的崩溃......
代码片段:
// calculate the size of a record, we use "size" as this is the number of bytes used to store on record
// other possibilities:
// .stride = number of bytes used to store one record and the added nul bytes to align to next memory bounds
// .alignment = number of bytes of alignment bounds
let sizeUInt16 : UInt64 = UInt64(MemoryLayout<UInt16>.size)
let sizeUInt64 : UInt64 = UInt64(MemoryLayout<UInt64>.size)
// get the data out of the asset catalog
if let countryBorderLineData = NSDataAsset(name: "CountryBorderLine data", bundle: Bundle.main)?.data {
// the read buffers, one for each expected data type
var dataReadBufferUInt16 : UInt16 = 0
var dataReadBufferUInt64 : UInt64 = 0
// read the string with the entry comment
// read the length of the string
(countryBorderLineData as NSData).getBytes(&dataReadBufferUInt16, range: NSRange(location: nextLocation,
length: Int(sizeUInt16) ))
// advance the pointer
nextLocation += Int(sizeUInt16)
// take the number of items we should read
var numberOfItemsToRead : Int = Int(dataReadBufferUInt16)
// check if this is not an empty string
if numberOfItemsToRead > 0 {
// target buffer of the string
var UTF16Array : [UInt16] = []
// loop to read all content
for _ in 0 ..< numberOfItemsToRead {
// read next string element
(countryBorderLineData as NSData).getBytes(&dataReadBufferUInt16, range: NSRange(location: nextLocation,
length: Int(sizeUInt16) ))
// advance the pointer
nextLocation += Int(sizeUInt16)
// append read string element to the array
UTF16Array.append(dataReadBufferUInt16)
}
// convert the read array into a string
let resultString = String(utf16CodeUnits: UTF16Array, count: UTF16Array.count)
}
// read the number of countries
(countryBorderLineData as NSData).getBytes(&dataReadBufferUInt64, range: NSRange(location: nextLocation,
length: Int(sizeUInt64) ))
// advance the pointer
nextLocation += Int(sizeUInt64)
// This line SOMETIMES crashes (see crash subset of crash report)
let numberOfCountries = Int(dataReadBufferUInt64)
...
}
这部分崩溃报告显示了错误
Date/Time: 2019-08-28 22:00:06.5042 +0200
Launch Time: 2019-08-28 22:00:02.2638 +0200
OS Version: iPhone OS 12.4 (16G77)
Baseband Version: 1.06.02
Report Version: 104
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x8000000000000010
VM Region Info: 0x8000000000000010 is not in any region. Bytes after previous region: 9223372025580486673
REGION TYPE START - END [ VSIZE] PRT/MAX SHRMOD REGION DETAIL
MALLOC_NANO 0000000280000000-00000002a0000000 [512.0M] rw-/rwx SM=PRV
--->
UNUSED SPACE AT END
Termination Signal: Segmentation fault: 11
Termination Reason: Namespace SIGNAL, Code 0xb
Terminating Process: exc handler [22974]
Triggered by Thread: 3
此类的所有方法都在以下 GCD 队列中调用:
let myQueueForBorderLines : DispatchQueue = DispatchQueue(
label: "appName.myQueueForBorderLines", qos: .userInitiated)
所使用的数据结构等仅由此类方法读取和管理，因此我认为这不是多线程问题。
最佳答案
更新
在知道旧代码中的 numberOfBytesToRead 不是问题的原因后，我现在可以向您展示 Data 的推荐用法。
let sizeUInt16 = MemoryLayout<UInt16>.size
let sizeUInt64 = MemoryLayout<UInt64>.size
// get the data out of the asset catalog
if let countryBorderLineData = NSDataAsset(name: "CountryBorderLine data", bundle: Bundle.main)?.data {
var nextLocation = 0
// the read buffers, one for each expected data type
var dataReadBufferUInt16: UInt16 = 0
var dataReadBufferUInt64: UInt64 = 0
// read the string with the entry comment
// read the length of the string
_ = withUnsafeMutableBytes(of: &dataReadBufferUInt16) {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += Int(sizeUInt16)
// take the number of items we should read
let numberOfItemsToRead = Int(dataReadBufferUInt16)
// check if this is not an empty string
if numberOfItemsToRead > 0 {
// target buffer of the string
var utf16Array: [UInt16] = Array(repeating: 0, count: numberOfItemsToRead)
utf16Array.withUnsafeMutableBufferPointer {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += numberOfItemsToRead * sizeUInt16
// convert the read array into a string
let resultString = String(utf16CodeUnits: utf16Array, count: utf16Array.count)
print(resultString)
}
// read the number of countries
_ = withUnsafeMutableBytes(of: &dataReadBufferUInt64) {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += sizeUInt64
// This line SOMETIMES crashes (see crash subset of crash report)
let numberOfCountries = Int(dataReadBufferUInt64)
//...
}
Swift.Data 的实现最近发生了变化，因此它可能会导致一些问题，但可能性不高(略高于非常不可能)。
如果您的代码在多线程上下文中运行，那可能会导致有时会崩溃。
无论如何，当您显示更多上下文时，我会检查它并再次更新我的答案。
旧答案
这取决于您的组织方式(您最好显示 NSDataAsset 的规范)，但是您的代码使用此循环消耗 numberOfBytesToRead * sizeUInt16 字节:
// loop to read all content
for _ in 0 ..< numberOfBytesToRead {
//...
// advance the pointer
nextLocation += Int(sizeUInt16)
//...
}
在此循环之后，nextLocation 可能指向某个未知位置，
这可能:
- 超出您的 countryBorderLineData 的有效范围
- 导致 Int(dataReadBufferUInt64) 溢出
- ...
循环遍历每个 UTF-16 代码点并不是读取 UTF-16 字符串的有效方法。
我会将您的代码重写为:
let sizeUInt16 = MemoryLayout<UInt16>.size
let sizeUInt64 = MemoryLayout<UInt64>.size
if let countryBorderLineData = data {
var nextLocation = 0
// the read buffers, one for each expected data type
var dataReadBufferUInt16: UInt16 = 0
var dataReadBufferUInt64: UInt64 = 0
// read the string with the entry comment
// read the length of the string
_ = withUnsafeMutableBytes(of: &dataReadBufferUInt16) {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += sizeUInt16
// take the number of bytes we should read
let numberOfBytesToRead = Int(dataReadBufferUInt16)
// check if this is not an empty string
if numberOfBytesToRead > 0 {
assert(numberOfBytesToRead.isMultiple(of: sizeUInt16))
// target buffer of the string
var utf16Array: [UInt16] = Array(repeating: 0, count: numberOfBytesToRead/sizeUInt16)
utf16Array.withUnsafeMutableBufferPointer {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += numberOfBytesToRead
// convert the read array into a string
let resultString = String(utf16CodeUnits: utf16Array, count: utf16Array.count)
print(resultString)
}
// read the number of countries
_ = withUnsafeMutableBytes(of: &dataReadBufferUInt64) {bufPtr in
countryBorderLineData.copyBytes(to: bufPtr, from: nextLocation...)
}
// advance the pointer
nextLocation += sizeUInt64
// This line SOMETIMES crashes (see crash subset of crash report)
let numberOfCountries = Int(dataReadBufferUInt64)
//...
}
我的猜测可能是错误的，上面的代码无法解决您的问题，在这种情况下，请提供有关您的数据的更多信息，我可以更正我的答案。
关于ios - 从 NSDataAsset 读取时偶尔崩溃，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57715807/