It's not obvious and may be related only to some specific versions of ImageMagick (tested only for 6.7.7 and 6.8.9), but $cols and $rows must be a positive non-zero value.
<?php
$image = new Imagick();
$image->newImage(0, 100, new ImagickPixel('red'));
$image->setImageFormat('png');
file_put_contents('image.png', $image);
?>
In this case imagemagick will crash without throwing any exception and you'll get something along the lines (in your apache error log or console output):
unable to acquire cache view `No such file or directory' @ fatal/cache-view.c/AcquireAuthenticCacheView/121.
This might be the case when you calculate $cols and $rows (say, based on user input and predefined target image DPI):
<?php
$image = new Imagick();
$img->newImage($userInput->getWidth() * $defaultPpi, $userInput->getHeight() * $defaultPpi, new ImagickPixel('white'));
?>
In this case if user requested image with 0.006 width (in inches), the code would work for $defaultPpi = 300 ppi, but would crash for
$defaultPpi = 72 ppi
