Re^3: Need to Generate Unique String

Guarenteed with a given process, but if multiple copies of the process are running, with time() limited to 1 second resolution?

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Comment on Re^3: Need to Generate Unique String

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Re^4: Need to Generate Unique String by hv (Prior) on Jul 30, 2004 at 12:13 UTC
Then the sleep() should ensure the pid is not reused within the same tick, so it should still remain unique. It does depend a bit on the precise sleep() implementation though; possibly safer (and a bit faster) would be: `my $t = time; select(undef, undef, undef, 0.1) while time <= $t; $unique = "$t$$";` [download] It also assumes a monotonically increasing time: if the sysadmin may correct a fast clock backwards, it would be very difficult to cope with. (Note that ntpd will adjust the time in increments of less than a second except when the clock error is "large"; once initially synchronised, a running system corrected by ntpd should never normally skip a full second forwards or backwards.) Hugo	[reply] [d/l]

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Re^4: Need to Generate Unique String
by hv (Prior) on Jul 30, 2004 at 12:13 UTC

Then the sleep() should ensure the pid is not reused within the same tick, so it should still remain unique.

It does depend a bit on the precise sleep() implementation though; possibly safer (and a bit faster) would be:

  my $t = time;
  select(undef, undef, undef, 0.1) while time <= $t;
  $unique = "$t$$";
[download]

It also assumes a monotonically increasing time: if the sysadmin may correct a fast clock backwards, it would be very difficult to cope with. (Note that ntpd will adjust the time in increments of less than a second except when the clock error is "large"; once initially synchronised, a running system corrected by ntpd should never normally skip a full second forwards or backwards.)

Hugo

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[d/l]