Make batch run --follow actually stream, and terminate#16
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--follow previously waited for the execution to finish and then printed its output in one block, which for a long job means staring at nothing for its whole duration. The first attempt at fixing that held a server-side follow open instead, and was worse: the server never closes a followed batch log, so the command hung until killed, and because it attached only after the execution left the queue it still showed everything at once. Tailing from a byte offset instead gives both properties. Output appears as it is produced -- verified against a job that prints every two seconds, and the lines arrive two seconds apart -- and the loop ends when the execution reaches a terminal state, which is where the answer to "is there more?" actually lives. The status is read before the log so a final read cannot miss anything written between the two. batch logs --follow uses the same loop, so it no longer hangs on an execution that has already finished.
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--followpreviously waited for the execution to finish and printed its output in one block — for a long job, that means staring at nothing for its whole duration.My first attempt held a server-side follow open instead, and was worse: the server never closes a followed batch log, so the command hung until killed, and because it only attached after the execution left the queue it still showed everything at once. Measured, all nine lines of a 16-second job arrived simultaneously at +49s, then it hung.
Tailing from a byte offset gives both properties:
Lines arrive ~2s apart, matching the job's
sleep(2). The loop ends when the execution reaches a terminal state — where the answer to "is there more?" actually lives. The status is read before the log, so the final read can't miss anything written between the two.batch logs --followuses the same loop, so it no longer hangs on an already-finished execution.