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4.7. Special probe points
The probe points
begin
and end
are defined by the translator to refer to the time of session startup and shutdown. There are no target variables available in either context.
4.7.1. begin
The
begin
probe is the start of the SystemTap session. All begin
probe handlers are run during the startup of the session. All global variables must be declared prior to this point.
4.7.2. end
The
end
probe is the end of the SystemTap session. All end
probes are run during the normal shutdown of a session, such as in the aftermath of an exit
function call, or an interruption from the user. In the case of an shutdown triggered by error, end
probes are not run.
4.7.3. begin and end probe sequence
begin
and end
probes are specified with an optional sequence number that controls the order in which they are run. If no sequence number is provided, the sequence number defaults to zero and probes are run in the order that they occur in the script file. Sequence numbers may be either positive or negative, and are especially useful for tapset writers who want to do initialization in a begin
probe. The following are examples.
# In a tapset file: probe begin(-1000) { ... } # In a user script: probe begin { ... }
The user script
begin
probe defaults to sequence number zero, so the tapset begin
probe will run first.
4.7.4. never
The
never
probe point is defined by the translator to mean never. Its statements are analyzed for symbol and type correctness, but its probe handler is never run. This probe point may be useful in conjunction with optional probes. See Section Section 4.1.4, “Optional probe points”.