Okay, then next question: what will happen if I call -write:maxLength:
on an NSOutputStream without having received a
NSStreamEventHasSpaceAvailable event? Is is guaranteed to block until
it has written at least one byte (assuming we're not dealing with a
fixed-length stream that has reached its capacity)?
I ask because, given that run-loop scheduling is not a guarantee
against blocking, I plan to put my NSOutputStream writing code in a
separate thread. It would be nice if I can ignore the stream events
entirely and just call -write:maxLength: whenever the thread receives
data to write, with something like:
- (void)sendLine: (NSString*)line {
NSUInteger bytesWritten = 0;
NSUInteger bytesToWrite = [line lengthOfBytesUsingEncoding:
NSUTF8StringEncoding];
char const * bytes = [line UTF8String];
while (bytesWritten < bytesToWrite) {
NSInteger result = [outputStream write: bytes + bytesWritten
maxLength: bytesToWrite - bytesWritten];
if (result <= 0)
@throw [NSException exceptionWithName: @"WriterThreadException"
reason: @"Error writing to output stream" userInfo: nil];
bytesWritten += result;
}
}
I would then use -performSelector:onThread:withObject:waitUntilDone:
from my main thread to queue data for sendLine to write. Is this a
viable approach?
-Michael
On May 8, 2008, at 2:58 AM, Stefan Haller wrote:
Michael Ash <[EMAIL PROTECTED]> wrote:
NSStream matches the semantics of the UNIX read/write calls. In both
cases, if you are informed that data or space is available, you can
issue a read or write for an arbitrary amount of data and be
guaranteed that it will not block.
I would have thought so too, but the NSStream documentation seems to
disagree (this is from the "Stream Programming Guide for Cocoa"
document):
: It should be pointed out that neither the polling nor run-loop
: scheduling approaches are airtight defenses against blocking. If the
: NSInputStream hasBytesAvailable method or the NSOutputStream
: hasSpaceAvailable method returns NO, it means in both cases that the
: stream definitely has no available bytes or space. However, if
either
: of these methods returns YES, it can mean that there is available
: bytes or space or that the only way to find out is to attempt a read
: or a write operation (which could lead to a momentary block). The
: NSStreamEventHasBytesAvailable and NSStreamEventHasSpaceAvailable
: stream events have identical semantics.
I'm not sure exactly what "momentary block" means here.
--
Stefan Haller
Ableton
http://www.ableton.com/
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