webgl/conformance/extensions/khr-parallel-shader-compile.html Updated in r274711, timing out in GLIB since, even with [ Slow ]. Checking the first loop of the test (~120), it seems the compile operations are not being offloaded to another thread, as there is a big wait in the compileShader calls. In the 7th iteration of the loop: extraCode size 2949120 shaderSource(vertexSource) took 18ms shaderSource(fragmentSource) took 17ms compileShader(vs) took 1460ms compileShader(fs) took 1392ms linkProgram(program) took 1ms This is causing the measuredCompileDuration to always be smaller than the threshold (500ms), as it's actually just a get operation, and the code never triggers the loop exit condition.