To use a speculation, an identifier returned from speculation
must be passed to the speculate
function in a clause before any data-recording actions. All subsequent data-recording actions in a clause containing a speculate
will be speculatively traced. The D compiler will generate a compile-time error if a call to speculate
follows data recording actions in a D probe clause. Therefore, clauses may contain speculative tracing or non-speculative tracing requests, but not both.
Aggregating actions, destructive actions, and the exit
action may never be speculative. Any attempt to take one of these actions in a clause containing a speculate
results in a compile-time error. A speculate
may not follow a speculate
: only one speculation is permitted per clause. A clause that contains only a speculate
will speculatively trace the default action, which is defined to trace only the enabled probe ID. See Chapter 10, Actions and Subroutines for a description of the default action.
Typically, you assign the result of speculation
to a thread-local variable and then use that variable as a subsequent predicate to other probes as well as an argument to speculate
. For example:
syscall::open:entry { self->spec = speculation(); } syscall::: /self->spec/ { speculate(self->spec); printf("this is speculative"); }