The 15.5ms attributed to re-reading the header on every reload is not that.
A timer around each stage says the cached dump reads in 0.33ms, the extraction
takes 3.3ms and the checks 0.55ms — about 4ms, once, in Session.create. The
rest of flan reload's delta is Load and Check over 256 more declarations, and
the +3.6ms a redefinition really pays is Check and Emit.redefinition against a
bigger program. A C-c C-c reads no header at all: eval's forms carry no import,
so no package is read.
Both cache levels anyway, because a long-lived process should pay nothing
twice. In the session, two tables: the dump by header, the declarations by
header and by what the package already declares. On disk, the existing cache
moved into the object cache directory beside the .o files. The in-memory key
is the path and the flags with no mtime, so a header edited mid-session is not
picked up until the session restarts — the rule a changed .c file follows, and
the rule that keeps new signatures from being checked against a process still
running the old layouts.
Measured: repeat import 3.65ms to nothing; flan reload unchanged, as it must
be, since it imports once per process.
Joseph Ferano
df1a43d3ac