NAME Data::HashMap::Shared - Type-specialized shared-memory hash maps for multiprocess access SYNOPSIS use Data::HashMap::Shared::II; # Create or open a shared map (file-backed mmap) my $map = Data::HashMap::Shared::II->new('/tmp/mymap.shm', 100000); # Keyword API (fastest) shm_ii_put $map, 42, 100; my $val = shm_ii_get $map, 42; # Method API $map->put(42, 100); my $v = $map->get(42); # Atomic counters (lock-free fast path) shm_ii_incr $map, 1; shm_ii_incr_by $map, 1, 10; # LRU cache (evicts least-recently-used when full) my $cache = Data::HashMap::Shared::II->new('/tmp/cache.shm', 100000, 1000); shm_ii_put $cache, 42, 100; # auto-evicts LRU entry if size > 1000 # TTL (entries expire after N seconds) my $ttl_map = Data::HashMap::Shared::II->new('/tmp/ttl.shm', 100000, 0, 60); shm_ii_put $ttl_map, 1, 10; # expires in 60s shm_ii_put_ttl $ttl_map, 2, 20, 5; # per-key: expires in 5s # Multiprocess if (fork() == 0) { my $child = Data::HashMap::Shared::II->new('/tmp/mymap.shm', 100000); shm_ii_incr $child, 1; # atomic increment visible to parent exit; } wait; DESCRIPTION Data::HashMap::Shared provides type-specialized hash maps stored in file-backed shared memory (mmap(MAP_SHARED)), enabling efficient multiprocess data sharing on Linux. Linux-only. Requires 64-bit Perl. Features * File-backed mmap for cross-process sharing * Futex-based read-write lock (fast userspace path) * Lock-free atomic counters (incr/decr under read lock) * Elastic capacity (starts small, grows/shrinks automatically) * Arena allocator for string storage in shared memory * Keyword API via XS::Parse::Keyword for maximum speed * Opt-in LRU eviction and per-key TTL (lock-free reads via clock eviction) * Stale lock recovery (automatic detection of dead lock holders via PID tracking) Variants Data::HashMap::Shared::I16 - int16 to int16 Data::HashMap::Shared::I32 - int32 to int32 Data::HashMap::Shared::II - int64 to int64 Data::HashMap::Shared::I16S - int16 to string Data::HashMap::Shared::I32S - int32 to string Data::HashMap::Shared::IS - int64 to string Data::HashMap::Shared::SI16 - string to int16 Data::HashMap::Shared::SI32 - string to int32 Data::HashMap::Shared::SI - string to int64 Data::HashMap::Shared::SS - string to string Constructor my $map = Data::HashMap::Shared::II->new($path, $max_entries); my $map = Data::HashMap::Shared::II->new($path, $max_entries, $max_size); my $map = Data::HashMap::Shared::II->new($path, $max_entries, $max_size, $ttl); my $map = Data::HashMap::Shared::II->new($path, $max_entries, $max_size, $ttl, $lru_skip); Creates or opens a shared hash map backed by file $path. $max_entries, $max_size, $ttl, and $lru_skip are used only when creating a new file; when opening an existing one, all parameters are read from the stored header and the constructor arguments are ignored. Multiple processes can open the same file simultaneously. Dies if the file exists but was created by a different variant or is corrupt. Optional $max_size enables LRU eviction: when the map reaches $max_size entries, the least-recently-used entry is evicted on insert. Set to 0 (default) to disable. LRU uses a clock/second-chance algorithm: "get" sets an accessed bit (lock-free, no write lock), and eviction gives a second chance to recently accessed entries before evicting. Optional $ttl sets a default time-to-live in seconds for all entries. Expired entries are lazily removed on access. Set to 0 (default) to disable. When TTL is active, "get" and "exists" check expiry. Optional $lru_skip (0-99, default 0) sets the probability (as a percentage) of skipping LRU promotion on "get". This reduces write-lock contention for Zipfian (power-law) access patterns where a small set of hot keys dominates reads. The LRU tail (eviction victim) is never skipped, preserving eviction correctness. Set to 0 for strict LRU ordering. Zero-cost when disabled: with both "$max_size=0" and "$ttl=0", the fast lock-free read path is used. The only overhead is a branch (predicted away). Sharding my $map = Data::HashMap::Shared::II->new_sharded($path_prefix, $shards, $max_entries, ...); Creates $shards independent maps (files "$path_prefix.0", "$path_prefix.1", ...) behind a single handle. Per-key operations automatically route to the correct shard via hash dispatch. Writes to different shards proceed in parallel with independent locks. All operations work transparently on sharded maps: "put", "get", "remove", "exists", "add", "update", "swap", "take", "incr", "cas", "get_or_set", "put_ttl", "touch", "persist", "set_ttl", "keys", "values", "items", "to_hash", "set_multi" (method only), "get_multi" (method only), "each", "pop", "shift", "drain", "clear", "flush_expired", "flush_expired_partial", "size", "stats" (method only), "reserve", and all diagnostic keywords. Cursors chain across shards automatically. "cursor_seek" routes to the correct shard based on key hash. $shards is rounded up to the next power of 2. API Replace "xx" with variant prefix: "i16", "i32", "ii", "i16s", "i32s", "is", "si16", "si32", "si", "ss". my $ok = shm_xx_put $map, $key, $value; # insert or overwrite my $ok = shm_xx_add $map, $key, $value; # insert only if key absent my $ok = shm_xx_update $map, $key, $value;# overwrite only if key exists my $old = shm_xx_swap $map, $key, $value; # put + return old value (undef if new) my $n = $map->set_multi($k, $v, ...); # batch put under single lock, returns count my @v = $map->get_multi($k1, $k2, ...); # batch get under single lock with prefetch pipeline my $v = shm_xx_get $map, $key; # returns undef if not found my $ok = shm_xx_remove $map, $key; # returns false if not found my $ok = shm_xx_exists $map, $key; # returns boolean my $s = shm_xx_size $map; my $m = shm_xx_max_entries $map; my @k = shm_xx_keys $map; my @v = shm_xx_values $map; my @items = shm_xx_items $map; # flat (k, v, k, v, ...) while (my ($k, $v) = shm_xx_each $map) { ... } # auto-resets at end shm_xx_iter_reset $map; shm_xx_clear $map; my $href = shm_xx_to_hash $map; my $v = shm_xx_get_or_set $map, $key, $default; # returns value Integer-value variants also have: my $n = shm_xx_incr $map, $key; # returns new value my $n = shm_xx_decr $map, $key; # returns new value my $ok = shm_xx_cas $map, $key, $expected, $desired; # compare-and-swap my $n = shm_xx_incr_by $map, $key, $delta; LRU/TTL operations (require TTL-enabled map for "put_ttl"): my $ok = shm_xx_put_ttl $map, $key, $value, $ttl_sec; # per-key TTL (0 = permanent); requires TTL-enabled map my $ms = shm_xx_max_size $map; # LRU capacity (0 = disabled) my $t = shm_xx_ttl $map; # default TTL in seconds my $r = shm_xx_ttl_remaining $map, $key; # seconds left (0 = permanent, undef if missing/expired/no TTL) my $ok = shm_xx_touch $map, $key; # reset TTL to default_ttl (LRU promotion still occurs on permanent entries); false if no TTL/LRU my $ok = shm_xx_persist $map, $key; # remove TTL, make key permanent; false on non-TTL maps my $ok = shm_xx_set_ttl $map, $key, $sec; # change TTL without changing value (0 = permanent); false on non-TTL maps my $n = shm_xx_flush_expired $map; # proactively expire all stale entries, returns count my ($n, $done) = shm_xx_flush_expired_partial $map, $limit; # gradual: scan $limit slots Atomic remove-and-return: my $v = shm_xx_take $map, $key; # remove key and return value (undef if missing) my ($k, $v) = shm_xx_pop $map; # remove+return from LRU tail / scan forward my ($k, $v) = shm_xx_shift $map; # remove+return from LRU head / scan backward my @kv = shm_xx_drain $map, $n; # remove+return up to N entries as flat (k,v,...) list "pop" and "shift" remove from opposite ends: "pop" takes the LRU tail (oldest / least recently used) while "shift" takes the LRU head (newest / most recently used). On non-LRU maps, "pop" scans forward and "shift" scans backward. "drain" removes in "pop" order (tail-first). Useful for work-queue patterns and batch processing. Cursors (independent iterators, allow nesting and removal during iteration): my $cur = shm_xx_cursor $map; # create cursor while (my ($k, $v) = shm_xx_cursor_next $cur) { ... } shm_xx_cursor_reset $cur; # restart from beginning shm_xx_cursor_seek $cur, $key; # position at specific key (best-effort across resize) # cursor auto-destroyed when out of scope "shm_xx_each" is also safe to use with "remove" during iteration. Resize/compaction is deferred until iteration ends. Diagnostics: my $cap = shm_xx_capacity $map; # current table capacity (slots) my $tb = shm_xx_tombstones $map; # tombstone count my $au = shm_xx_arena_used $map; # arena bytes used (0 for int-only) my $ac = shm_xx_arena_cap $map; # arena total capacity (0 for int-only) my $sz = shm_xx_mmap_size $map; # backing file size in bytes my $ok = shm_xx_reserve $map, $n; # pre-grow (false if exceeds max) my $ev = shm_xx_stat_evictions $map; # cumulative LRU eviction count my $ex = shm_xx_stat_expired $map; # cumulative TTL expiration count my $rc = shm_xx_stat_recoveries $map; # cumulative stale lock recovery count my $p = $map->path; # backing file path (method only) my $s = $map->stats; # hashref with all diagnostics in one call # stats keys: size, capacity, max_entries, tombstones, mmap_size, # arena_used, arena_cap, evictions, expired, recoveries, max_size, ttl "set_multi", "stats", "path", and "unlink" are method-only (no keyword form). File management: $map->unlink; # remove backing file (mmap stays valid) Data::HashMap::Shared::II->unlink($path); # class method form Crash Safety If a process dies (e.g., SIGKILL, OOM kill) while holding the write lock, other processes will detect the stale lock within 2 seconds via PID tracking and automatically recover. The writer's PID is encoded in the rwlock word itself (single atomic CAS, no crash window), so recovery is reliable even if the process is killed mid-acquisition. On timeout, waiters check "kill($pid, 0)" and CAS-release the lock if the holder is dead. Limitation: PID-based recovery assumes all processes share the same PID namespace. Cross-container sharing (different PID namespaces) is not supported. After recovery from a mid-mutation crash, the map data may be inconsistent. Calling "clear" after detecting a stale lock recovery is recommended for safety-critical applications. BENCHMARKS Throughput versus other shared-memory / on-disk solutions, 25K entries, single process, Linux x86_64. Run "perl -Mblib bench/vs.pl 25000" to reproduce. INTEGER KEY -> INTEGER VALUE (Shared::II) Rate BerkeleyDB LMDB Shared::II INSERT 31/s 31 46 184 LOOKUP 35/s 35 40 383 INCREMENT 16/s 16 18 165 STRING KEY -> STRING VALUE, SHORT (inline ≤7B, Shared::SS) Rate FastMmap BerkeleyDB LMDB SharedMem Shared::SS INSERT 11/s 11 26 40 62 130 LOOKUP 10/s 10 32 34 146 213 DELETE 14/s 14 18 -- 32 68 STRING KEY -> STRING VALUE, LONG (~50-100B, Shared::SS) Rate BerkeleyDB LMDB SharedMem Shared::SS INSERT 25/s 25 37 61 133 LOOKUP 30/s 30 33 125 229 LRU CACHE LOOKUP (25K entries, lock-free clock eviction) II plain 350/s II LRU 373/s (lock-free, ~6% faster via clock) SS plain 159/s SS LRU 159/s CROSS-PROCESS (25K SS entries, 2 processes) READS Shared::SS 3,250,000/s SharedMem 1,986,000/s LMDB 728,000/s WRITES Shared::SS 2,801,000/s SharedMem 826,000/s LMDB 95,000/s MIXED 50/50 Shared::SS 3,691,000/s SharedMem 1,963,000/s LMDB 211,000/s LMDB benchmarked with MDB_WRITEMAP|MDB_NOSYNC|MDB_NOMETASYNC|MDB_NORDAHEAD. BerkeleyDB with DB_PRIVATE|128MB cache. Key takeaways: * 10x faster lookups than LMDB for integer keys (lock-free seqlock path) * 1.5x faster than Hash::SharedMem for short string lookups (inline strings, no arena overhead) * 1.8x faster than Hash::SharedMem for long string lookups * 4.5x faster cross-process reads than LMDB; 3.4x faster writes than SharedMem * LRU reads are lock-free (clock eviction) — no overhead vs plain maps * Atomic "incr" is 9x faster than get+put on competitors * Strings ≤ 7 bytes stored inline in node (zero arena overhead) AUTHOR vividsnow LICENSE This is free software; you can redistribute it and/or modify it under the same terms as Perl itself.