Hi, I have an issue that COPY from a FIFO, which has no writers, could not be canceled, because COPY invokes AllocateFile() -> fopen() -> blocking open().
``` [postgres@s1 ~]$ mkfifo /tmp/test0 [postgres@s1 ~]$ /usr/local/pgsql/bin/psql test psql (11devel) Type "help" for help. test=# create table test(t text); CREATE TABLE test=# copy test from '/tmp/test0'; ^CCancel request sent ^CCancel request sent ^CCancel request sent ^CCancel request sent ^CCancel request sent ^CCancel request sent ... ``` Should we nonblocking open FIFO files? And a following question if we nonblocking open them, say there is a FIFO file, no one will write into it, and a utility calls `COPY FROM` it, should we just return `COPY 0` or wait writers? If we wait, then users have to interrupt or write an EOF into the FIFO after a timeout, I see some utilities do that, gptransfer for instance, just seems not right. My plan is to write a new function which nonblocking opens FIFOs just for COPY, and not waits writers, what do you think? -- Adam Lee
