NAME
Data::IntervalTree::Shared - shared-memory interval tree (overlap / stabbing queries)
SYNOPSIS
use Data::IntervalTree::Shared;
# up to 100_000 intervals
my $it = Data::IntervalTree::Shared->new(undef, 100_000);
$it->add($start, $end, $booking_id) for @bookings; # each interval carries an id
# which intervals contain a point?
my @at = $it->stab($t); # e.g. "what's booked at time $t"
# which intervals overlap a range?
my @ov = $it->overlaps($lo, $hi); # e.g. "any booking touching [$lo,$hi]"
printf "id %d: [%d, %d]\n", $_->{id}, $_->{lo}, $_->{hi} for @ov;
# share the index across processes via a backing file
my $shared = Data::IntervalTree::Shared->new("/tmp/bookings.it", 100_000);DESCRIPTION
An interval tree in shared memory: a set of integer intervals [lo, hi] that answers overlap and stabbing queries far faster than scanning every interval -- "which stored intervals contain point p?" and "which overlap the range [lo, hi]?". It complements Data::SegmentTree::Shared (range-aggregate over indexed positions) and Data::KDTree::Shared (multi-dimensional points): this one indexes a set of intervals for containment/overlap. Classic uses: scheduling and calendar conflict detection, IP-range to owner lookup, genomic feature overlap, and "what is active at time t".
Endpoints are signed 64-bit integers (timestamps, IP addresses, genomic coordinates -- exact, with no floating-point edge cases). Each interval carries a user-supplied 64-bit id (defaulting to its insertion index), returned with every match. Internally it is an augmented balanced binary search tree keyed by the low endpoint, each node caching the maximum high endpoint of its subtree so a query prunes whole subtrees that end before it.
Intervals are appended in O(1) and the balanced tree is bulk-built on the first query after any insert, so query recursion is O(log n + k) deep (k = matches) regardless of insertion order -- no risk of a degenerate, deep tree. Because the intervals live in a shared mapping, several processes build and query one index: any process that opens the same backing file, inherits the anonymous mapping across fork, or reopens a passed memfd sees the same intervals. A write-preferring futex rwlock with dead-process recovery guards mutation; once the tree is built, queries take only the read lock. Linux-only. Requires 64-bit Perl.
The index has a fixed capacity; adding beyond it croaks. Memory is capacity * 40 bytes for the intervals plus a build scratch of capacity * 4 bytes and a fixed header.
METHODS
Constructors
my $it = Data::IntervalTree::Shared->new($path, $capacity, $mode);
my $it = Data::IntervalTree::Shared->new(undef, $capacity);
my $it = Data::IntervalTree::Shared->new_memfd($name, $capacity);
my $it = Data::IntervalTree::Shared->new_from_fd($fd);$capacity is the maximum number of intervals (1..2^24). new and new_memfd croak on an out-of-range $capacity. When reopening an existing file or memfd the stored geometry wins and the caller's argument is ignored. An optional file mode may be passed as the last argument to new (e.g. 0660) for cross-user sharing; it defaults to 0600 (owner-only).
Adding intervals
my $i = $it->add($lo, $hi); # id defaults to the insertion index
my $i = $it->add($lo, $hi, $id); # attach an explicit 64-bit id
$it->build; # (optional) force a rebuild nowadd appends one interval with integer endpoints $lo <= $hi (croaks otherwise) and an optional integer $id, returning its insertion index; it croaks if the tree is full. Intervals are treated as closed (both endpoints inclusive). build forces the balanced tree to be (re)built immediately; you rarely need it, since queries build automatically after inserts.
Queries
my @at = $it->stab($point); # intervals containing $point (lo <= p <= hi)
my @ov = $it->overlaps($lo, $hi); # intervals overlapping [$lo, $hi]stab returns every stored interval that contains the point $point. overlaps returns every stored interval that intersects the closed range [$lo, $hi] (i.e. interval.lo <= $hi and interval.hi >= $lo); $lo > $hi croaks. Both return a list of hash references { id => ..., lo => ..., hi => ... }, sorted by lo ascending. A point stab is exactly overlaps($p, $p).
Introspection and lifecycle
$it->count; # number of intervals added
$it->capacity; # maximum number of intervals
$it->clear; # remove all intervals
$it->stats; # { count, capacity, dirty, ops, mmap_size }
$it->path; $it->memfd; $it->sync; $it->unlink;clear empties the index. sync flushes the mapping to its backing store (a no-op for anonymous and memfd trees); unlink removes the backing file (also callable as Class->unlink($path)); path returns the backing path (undef for anonymous, memfd, or fd-reopened trees) and memfd the backing descriptor.
SHARING ACROSS PROCESSES
The index lives in a shared mapping, shared the same three ways as the rest of the family: a backing file, an anonymous mapping inherited across fork, or a memfd passed to an unrelated process and reopened with new_from_fd($fd). Any process can add intervals; the first query after an add rebuilds the shared tree once (under the write lock), and subsequent queries run concurrently under the read lock.
SECURITY
Backing files are created with mode 0600 (owner-only) by default; pass an explicit octal mode (e.g. 0660) as the last argument to new for cross-user sharing. The file is opened with O_NOFOLLOW and O_EXCL, and the header is validated on attach. Any process granted write access is trusted not to corrupt the mapping.
CRASH SAFETY
Mutation is guarded by a futex-based write-preferring rwlock with PID-encoded ownership and dead-owner recovery. Adds are short bounded appends and the bulk build runs entirely under the write lock, so a crash leaves the index consistent up to the last completed operation (a crash mid-build simply leaves it marked for rebuild). Limitation: PID reuse is not detected (very unlikely in practice).
Reader-slot exhaustion (slotless readers): dead-process recovery attributes a crashed lock holder's contribution through its reader-slot. The slot table holds 1024 entries (one per concurrent reader process). If more than that many reader processes share one mapping at once, a reader that cannot claim a slot proceeds "slotless" -- it still takes the read lock but leaves no per-process record. If such a slotless reader is then killed while holding the read lock, its share of the lock cannot be attributed to a dead process, so writer recovery cannot reclaim it and writers may block until the mapping is recreated. Reaching this needs more than 1024 concurrent reader processes on one mapping plus a crash in the brief read-lock window; the dead-process slot reclaim keeps the table from filling with stale entries, so in practice it is very unlikely.
SEE ALSO
Data::SegmentTree::Shared (range-aggregate over indexed positions), Data::KDTree::Shared (multi-dimensional point index), and the rest of the Data::*::Shared family.
AUTHOR
vividsnow
LICENSE
This is free software; you can redistribute it and/or modify it under the same terms as Perl itself.