perl - 为什么%main::的符号表中有几个c文件？

Question

'_<perlmain.c' => *{'::_<perlmain.c'},
'_</usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/auto/Data/Dumper/Dumper.so' => *{'::_</usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/auto/Data/Dumper/Dumper.so'},
'_<universal.c' => *{'::_<universal.c'},
'_<xsutils.c' => *{'::_<xsutils.c'},
...

为什么它们在 %main::的符号表中，它们什么时候有用？

Answer 1

要重复问题的输出，请运行

#! /usr/bin/env perl
use Data::Dumper;
print Dumper \%main::;

您看到的条目已插入 gv_fetchfile_flags :

/* This is where the debuggers %{"::_<$filename"} hash is created */
tmpbuf[0] = '_';
tmpbuf[1] = '<';
memcpy(tmpbuf + 2, name, namelen);
gv = *(GV**)hv_fetch(PL_defstash, tmpbuf, tmplen, TRUE);
if (!isGV(gv)) {
    gv_init(gv, PL_defstash, tmpbuf, tmplen, FALSE);
#ifdef PERL_DONT_CREATE_GVSV
    GvSV(gv) = newSVpvn(name, namelen);
#else
    sv_setpvn(GvSV(gv), name, namelen);
#endif
}

这被多次调用 newXS 作为 boot process in S_parse_body 的一部分.

boot_core_PerlIO();
boot_core_UNIVERSAL();
boot_core_mro();

请注意，您还会看到 perlio.c 的条目, universal.c , 和 mro.c在输出中。

Debugger Internals perldebguts documentation的部分解释它们的用途:

For example, whenever you call Perl's built-in caller function from the package DB, the arguments that the corresponding stack frame was called with are copied to the @DB::args array. These mechanisms are enabled by calling Perl with the -d switch. Specifically, the following additional features are enabled (cf. $^P in perlvar):

• …
• Each array @{"_<$filename"} holds the lines of $filename for a file compiled by Perl. The same is also true for evaled strings that contain subroutines, or which are currently being executed. The $filename for evaled strings looks like (eval 34). Code assertions in regexes look like (re_eval 19).
• Each hash %{"_<$filename"} contains breakpoints and actions keyed by line number. Individual entries (as opposed to the whole hash) are settable. Perl only cares about Boolean true here, although the values used by perl5db.pl have the form "$break_condition\0$action".
  The same holds for evaluated strings that contain subroutines, or which are currently being executed. The $filename for evaled strings looks like (eval 34) or (re_eval 19) .
• Each scalar ${"_<$filename"} contains "_<$filename". This is also the case for evaluated strings that contain subroutines, or which are currently being executed. The $filename for evaled strings looks like (eval 34) or (re_eval 19).
• After each required file is compiled, but before it is executed, DB::postponed(*{"_<$filename"}) is called if the subroutine DB::postponed exists. Here, the $filename is the expanded name of the required file, as found in the values of %INC.
• …