问题
I'm trying to use a Pipe's fileHandleForReading's readabilityHandler to read both the standardOutput and standardError of a Process. However, the moment the terminationHandler is called is actually before the moment my readabilityHandler
is called for the first time.
I'm not sure why the process does this, but it means I'm not getting all the data, because I assume process termination means all output has been flushed to the pipe. Since this isn't the case, is there a way for me to tell when there is no more output to be read? I assume that involves checking if a FileHandle is still open, but I don't see an API for that.
Here's an example of the basic idea of what my code looks like:
let stdOutPipe = Pipe()
let stdErrPipe = Pipe()
stdOutPipe.fileHandleForReading.readabilityHandler = { stdOutFileHandle in
let stdOutPartialData = stdOutFileHandle.readDataToEndOfFile()
guard !stdOutPartialData.isEmpty else {
print("Time to read, but nothing to be read?") // happens a lot
return
}
self.tempStdOutStorage.append(stdOutPartialData)
}
stdErrPipe.fileHandleForReading.readabilityHandler = { stdErrFileHandle in
let stdErrPartialData = stdErrFileHandle.readDataToEndOfFile()
guard !stdErrPartialData.isEmpty else {
print("Time to read, but nothing to be read?") // happens a lot
return
}
self.tempStdErrStorage.append(stdErrPartialData)
}
process.standardOutput = stdOutPipe
process.standardError = stdErrPipe
process.terminationHandler = { process in
notifyOfCompleteRead(stdOut: self.tempStdOutStorage, stdErr: self.tempStdErrStorage)
}
mySpecializedDispatchQueue.async(execute: process.launch)
回答1:
In the readabilityHandler
you should use availableData
to get the
currently available data without blocking. Empty available data indicates EOF
on the file handle, in that case the readability handler should be removed.
A dispatch group can be used to wait for EOF on both standard output and standard error after the process has finished.
Example:
let group = DispatchGroup()
group.enter()
stdOutPipe.fileHandleForReading.readabilityHandler = { stdOutFileHandle in
let stdOutPartialData = stdOutFileHandle.availableData
if stdOutPartialData.isEmpty {
print("EOF on stdin")
stdOutPipe.fileHandleForReading.readabilityHandler = nil
group.leave()
} else {
tempStdOutStorage.append(stdOutPartialData)
}
}
group.enter()
stdErrPipe.fileHandleForReading.readabilityHandler = { stdErrFileHandle in
let stdErrPartialData = stdErrFileHandle.availableData
if stdErrPartialData.isEmpty {
print("EOF on stderr")
stdErrPipe.fileHandleForReading.readabilityHandler = nil
group.leave()
} else {
tempStdErrStorage.append(stdErrPartialData)
}
}
process.standardOutput = stdOutPipe
process.standardError = stdErrPipe
process.launch()
process.terminationHandler = { process in
group.wait()
print("OUTPUT:", String(data: tempStdOutStorage, encoding: .utf8)!)
print("ERROR: ", String(data: tempStdErrStorage, encoding: .utf8)!)
}
来源:https://stackoverflow.com/questions/52335435/how-can-i-tell-when-a-filehandle-has-nothing-left-to-be-read