Using NSTask and NSPipe causes 100% CPU usage

cocoa, macos, nspipe, nstask, objective-c

Solution

File handle left open?

@interface AppDelegate ()
@property (nonatomic) NSTask *task;
@property (nonatomic) NSPipe *pipe;
@end

@implementation AppDelegate
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    self.pipe = [NSPipe pipe];
    self.pipe.fileHandleForReading.readabilityHandler = ^(NSFileHandle *h) {
        NSLog(@"Read: %@", [h readDataToEndOfFile]);
        [h closeFile];
    };

    self.task = [[NSTask alloc] init];
    self.task.launchPath = @"/bin/bash";
    self.task.arguments = @[@"-c", @"echo test"];
    self.task.standardOutput = self.pipe;
    [self.task launch];
}

Closing the file on the `NSFileHandle` `h` seems to return your CPU usage to normal.

Problem

I'm trying to run a simple bash script using NSTask and direct the output to a text view. Once the task is executed, the CPU usage of my app is 100%, even though it's a simple `echo` (for now). I created a completely fresh project to isolate the issue: ``` @interface AppDelegate () @property (nonatomic) NSTask *task; @property (nonatomic) NSPipe *pipe; @end @implementation AppDelegate - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { self.pipe = [NSPipe pipe]; self.pipe.fileHandleForReading.readabilityHandler = ^(NSFileHandle *h) { NSLog(@"Read: %@", [h readDataToEndOfFile]); }; self.task = [[NSTask alloc] init]; self.task.launchPath = @"/bin/bash"; self.task.arguments = @[@"-c", @"echo test"]; self.task.standardOutput = self.pipe; [self.task launch]; } @end ``` It is correctly executed and the output (as an `NSData`) is logged with `NSLog`: ``` PipeTest[3933:2623] Read: <74657374 0a> ``` However the CPU usage stays at 100% until I terminate my app. EDIT: A Time Profiler test returns the list below, but I'm not sure how to interpret this.

Original source