You can use the -j1 argument to gclient sync, to make it run one
process at a time. This should produce single-threaded output, which
is not garbled, and which should end when the sync runs into errors.
It looks like this is a dartium checkout, not just a dart repo
checkout. These are larger, and check out more repos. I can try it
locally. What is the gclient config command you used to produce this
output?
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William Hesse