On Apr 3, 2009, at 11:10 AM, Michael Ash wrote:
On Fri, Apr 3, 2009 at 9:36 AM, Michael Domino
<michael.dom...@identityfinder.com> wrote:
I have a task prepared and launched with the code below, and when
it returns
(in this situation that status code returned from terminationStatus
is 0),
it hangs in availableData, never to return. [...]
messagePipeError = [NSPipe pipe];
messagePipeOutput = [NSPipe pipe];
[task setLaunchPath:@"/usr/bin/
hdiutil"];
[task setArguments:[NSArray
arrayWithObjects:@"info", nil]];
[task
setStandardError:messagePipeError];
[task
setStandardOutput:messagePipeOutput];
[task launch];
[task waitUntilExit];
status = [task terminationStatus];
NSData *messageDataError = [[messagePipeError
fileHandleForReading] availableData];
messageError = [[[NSString alloc]
initWithData:messageDataError encoding:NSUTF8StringEncoding]
autorelease];
I don't know if this is the cause of your problem or not, but never,
ever do this. Don't call waitUntilExit before you read. Pipes have a
small buffer (4kB?) and if it fills up then further writes will block.
This means that if you do a waitUntilExit while the subprocess is
writing more data than the pipe can buffer, you'll deadlock. The
subprocess will be waiting for you to read data before it can
continue, and you will be waiting for it to exit before you read data.
Read all data (using readDataToEndOfFile or equivalent) *before* you
do waitUntilExit.
And, since you have two pipes, you're going to have to read from both
simultaneously. Otherwise, you still have a chance for deadlock, if
you're blocking reading on one handle while the subprocess is blocking
waiting for the other pipe to be drained.
This is best done using the asynchronous methods of NSFileHandle.
Cheers,
Ken
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