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在我的应用程序中，按钮触击从Internet站点下载数据。该网站是包含二进制数据的链接列表。有时，第一个链接可能不包含正确的数据。在这种情况下，应用程序将获取数组中的下一个链接并从中获取数据。链接是正确的。Swift：从url下载数据会导致semaphore_wait_trap冻结
我遇到的问题是，当我点击按钮时，应用程序频繁（并非总是）会冻结数秒。 5-30秒后，正常解冻并下载工具。我明白，有些东西阻止了主线程。当停止在Xcode的过程中，我得到这个（semaphore_wait_trap指出）：
这是我要做的事：
// Button Action
@IBAction func downloadWindNoaa(_ sender: UIButton)
{
// Starts activity indicator
startActivityIndicator()
// Starts downloading and processing data
// Either use this
DispatchQueue.global(qos: .default).async
{
DispatchQueue.main.async
{
self.downloadWindsAloftData()
}
}
// Or this - no difference.
//downloadWindsAloftData()
}
}
func downloadWindsAloftData()
{
// Creates a list of website addresses to request data: CHECKED.
self.listOfLinks = makeGribWebAddress()
// Extract and save the data
saveGribFile()
}
// This downloads the data and saves it in a required format. I suspect, this is the culprit
func saveGribFile()
{
// Check if the links have been created
if (!self.listOfLinks.isEmpty)
{
/// Instance of OperationQueue
queue = OperationQueue()
// Convert array of Strings to array of URL links
let urls = self.listOfLinks.map { URL(string: $0)! }
guard self.urlIndex != urls.count else
{
NSLog("report failure")
return
}
// Current link
let url = urls[self.urlIndex]
// Increment the url index
self.urlIndex += 1
// Add operation to the queue
queue.addOperation {() -> Void in
// Variables for Request, Queue, and Error
let request = URLRequest(url: url)
let session = URLSession.shared
// Array of bytes that will hold the data
var dataReceived = [UInt8]()
// Read data
let task = session.dataTask(with: request) {(data, response, error) -> Void in
if error != nil
{
print("Request transport error")
}
else
{
let response = response as! HTTPURLResponse
let data = data!
if response.statusCode == 200
{
//Converting data to String
dataReceived = [UInt8](data)
}
else
{
print("Request server-side error")
}
}
// Main thread
OperationQueue.main.addOperation(
{
// If downloaded data is less than 2 KB in size, repeat the operation
if dataReceived.count <= 2000
{
self.saveGribFile()
}
else
{
self.setWindsAloftDataFromGrib(gribData: dataReceived)
// Reset the URL Index back to 0
self.urlIndex = 0
}
}
)
}
task.resume()
}
}
}
// Processing data further
func setWindsAloftDataFromGrib(gribData: [UInt8])
{
// Stops spinning activity indicator
stopActivityIndicator()
// Other code to process data...
}
// Makes Web Address
let GRIB_URL = "http://xxxxxxxxxx"
func makeGribWebAddress() -> [String]
{
var finalResult = [String]()
// Main address site
let address1 = "http://xxxxxxxx"
// Address part with type of data
let address2 = "file=gfs.t";
let address4 = "z.pgrb2.1p00.anl&lev_250_mb=on&lev_450_mb=on&lev_700_mb=on&var_TMP=on&var_UGRD=on&var_VGRD=on"
let leftlon = "0"
let rightlon = "359"
let toplat = "90"
let bottomlat = "-90"
// Address part with coordinates
let address5 = "&leftlon="+leftlon+"&rightlon="+rightlon+"&toplat="+toplat+"&bottomlat="+bottomlat
// Vector that includes all Grib files available for download
let listOfFiles = readWebToString()
if (!listOfFiles.isEmpty)
{
for i in 0..<listOfFiles.count
{
// Part of the link that includes the file
let address6 = "&dir=%2F"+listOfFiles[i]
// Extract time: last 2 characters
let address3 = listOfFiles[i].substring(from:listOfFiles[i].index(listOfFiles[i].endIndex, offsetBy: -2))
// Make the link
let addressFull = (address1 + address2 + address3 + address4 + address5 + address6).trimmingCharacters(in: .whitespacesAndNewlines)
finalResult.append(addressFull)
}
}
return finalResult;
}
func readWebToString() -> [String]
{
// Final array to return
var finalResult = [String]()
guard let dataURL = NSURL(string: self.GRIB_URL)
else
{
print("IGAGribReader error: No URL identified")
return []
}
do
{
// Get contents of the page
let contents = try String(contentsOf: dataURL as URL)
// Regular expression
let expression : String = ">gfs\\.\\d+<"
let range = NSRange(location: 0, length: contents.characters.count)
do
{
// Match the URL content with regex expression
let regex = try NSRegularExpression(pattern: expression, options: NSRegularExpression.Options.caseInsensitive)
let contentsNS = contents as NSString
let matches = regex.matches(in: contents, options: [], range: range)
for match in matches
{
for i in 0..<match.numberOfRanges
{
let resultingNS = contentsNS.substring(with: (match.rangeAt(i))) as String
finalResult.append(resultingNS)
}
}
// Remove "<" and ">" from the strings
if (!finalResult.isEmpty)
{
for i in 0..<finalResult.count
{
finalResult[i].remove(at: finalResult[i].startIndex)
finalResult[i].remove(at: finalResult[i].index(before: finalResult[i].endIndex))
}
}
}
catch
{
print("IGAGribReader error: No regex match")
}
}
catch
{
print("IGAGribReader error: URL content is not read")
}
return finalResult;
}
我一直在试图解决这个问题，在过去几个星期但徒劳无益。任何帮助将非常感激！
无关，这里使用操作队列是完全不必要的，效率低下。您正在为每个请求新的队列（这是奇怪的......那是什么，只会曾经有一个操作？“排队”的目的），然后加入网络请求的起点（但响应的不接收并处理它）到该队列。我建议完全丢失这个操作队列的东西。调用'downloadWindsAloftData'，异步方法本身的嵌套的调度也很奇怪。 – Rob
Rob。对不起，添加了代码。我觉得没有队列，我没有设法执行我的任务，如果没有加载正确的数据，这将进入下一个链接。你会建议什么？ –
这里的自定义操作队列代码应该被删除。只需创建你的'URLSessionTask'和'resume'，它的完成处理程序就会在后台线程上异步运行。而你在'OperationQueue.main.addOperation {...}的位置，你应该只做'DispatchQueue.main.async {...}'。如果您的异步代码有问题，请创建一个简单的[MCVE]（http://stackoverflow.com/help/mcve）并针对该主题创建一个新问题。 – Rob