From c386663dd9ffec6ebbe64e7bb5096ee3df7d273d Mon Sep 17 00:00:00 2001
From: Eric Wong <e@yhbt.net>
Date: Fri, 24 Jul 2020 05:55:49 +0000
Subject: v2writable: introduce idx_stack

This avoids pinning a potentially large chunk of memory from
`git-log --reverse' into RAM (or triggering less predictable
swap behavior).  Instead it uses a contiguous temporary file
with a fixed-size record for every blob we'll need to index.
---
 lib/PublicInbox/IdxStack.pm | 52 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 lib/PublicInbox/IdxStack.pm

(limited to 'lib/PublicInbox/IdxStack.pm')

diff --git a/lib/PublicInbox/IdxStack.pm b/lib/PublicInbox/IdxStack.pm
new file mode 100644
index 00000000..b43b8064
--- /dev/null
+++ b/lib/PublicInbox/IdxStack.pm
@@ -0,0 +1,52 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# temporary stack for public-inbox-index
+package PublicInbox::IdxStack;
+use v5.10.1;
+use strict;
+use Fcntl qw(:seek);
+use constant FMT => eval { pack('Q', 1) } ? 'A1QQH*' : 'A1IIH*';
+
+# start off in write-only mode
+sub new {
+	open(my $io, '+>', undef) or die "open: $!";
+	bless { wr => $io, latest_cmt => $_[1] }, __PACKAGE__
+}
+
+# file_char = [a|m]
+sub push_rec {
+	my ($self, $file_char, $at, $ct, $blob_oid) = @_;
+	my $rec = pack(FMT, $file_char, $at, $ct, $blob_oid);
+	$self->{rec_size} //= length($rec);
+	print { $self->{wr} } $rec or die "print: $!";
+	$self->{tot_size} += length($rec);
+}
+
+sub num_records {
+	my ($self) = @_;
+	$self->{rec_size} ? $self->{tot_size} / $self->{rec_size} : 0;
+}
+
+# switch into read-only mode and returns self
+sub read_prepare {
+	my ($self) = @_;
+	my $io = $self->{rd} = delete($self->{wr});
+	$io->flush or die "flush: $!";
+	$self;
+}
+
+sub pop_rec {
+	my ($self) = @_;
+	my $sz = $self->{rec_size} or return;
+	my $rec_pos = $self->{tot_size} -= $sz;
+	return if $rec_pos < 0;
+	my $io = $self->{rd};
+	seek($io, $rec_pos, SEEK_SET) or die "seek: $!";
+	my $r = read($io, my $buf, $sz);
+	defined($r) or die "read: $!";
+	$r == $sz or die "read($r != $sz)";
+	unpack(FMT, $buf);
+}
+
+1;
-- 
cgit v1.2.3-24-ge0c7