Add entry caching to archive file systems

src/main.zig

@@ -11,7 +11,9 @@ const sys = @import("./sys.zig");
 /// Entry point.
 ///
 pub fn main() anyerror!void {
-    return nosuspend await async sys.runGraphics(anyerror, run);
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+
+    return nosuspend await async sys.runGraphics(gpa.allocator(), anyerror, run);
 }
 
 test {

src/sys.zig

@@ -35,6 +35,7 @@ pub const AppContext = opaque {
     /// Internal state of the event loop hidden from the API consumer.
     ///
     const Implementation = struct {
+        user_path_prefix: [*]u8,
         data_file_system: FileSystem,
         user_file_system: FileSystem,
         message_semaphore: *ext.SDL_sem,
@@ -104,6 +105,7 @@ pub const AppContext = opaque {
 
             ext.SDL_DestroyMutex(implementation.message_mutex);
             ext.SDL_DestroySemaphore(implementation.message_semaphore);
+            ext.SDL_free(implementation.user_path_prefix);
         }
 
         ///
@@ -134,14 +136,25 @@ pub const AppContext = opaque {
         ///
         /// Returns the created [Implementation] value on success or [InitError] on failure.
         ///
-        fn init(data_archive_file_access: FileAccess,
-            user_path_prefix: []const u8) InitError!Implementation {
+        fn init(allocator: std.mem.Allocator,
+            data_archive_file_access: FileAccess) InitError!Implementation {
+
+            const user_path_prefix = ext.SDL_GetPrefPath("ona", "ona") orelse
+                return error.OutOfMemory;
 
             return Implementation{
+                .user_file_system = .{.native = .{.path_prefix =
+                    user_path_prefix[0 .. std.mem.len(user_path_prefix)]}},
+
                 .message_semaphore = ext.SDL_CreateSemaphore(0) orelse return error.OutOfSemaphores,
                 .message_mutex = ext.SDL_CreateMutex() orelse return error.OutOfMutexes,
-                .data_file_system = .{.archive = .{.file_access = data_archive_file_access}},
-                .user_file_system = .{.native = .{.path_prefix = user_path_prefix}},
+                .user_path_prefix = user_path_prefix,
+
+                .data_file_system = .{.archive = .{
+                    .file_access = data_archive_file_access,
+                    .index_cache = try FileSystem.ArchiveIndexCache.init(allocator),
+                }},
+
                 .message_thread = null,
             };
         }
@@ -351,7 +364,7 @@ pub const FileSystem = union(enum) {
 
     archive: struct {
         file_access: FileAccess,
-        index_cache: *table.Dynamic([]const u8, ArchiveEntry, table.string_context),
+        index_cache: ArchiveIndexCache,
 
         entry_table: [max_open_entries]ArchiveEntry =
             std.mem.zeroes([max_open_entries]ArchiveEntry),
@@ -368,6 +381,8 @@ pub const FileSystem = union(enum) {
         cursor: u64,
     };
 
+    const ArchiveIndexCache = table.Hashed([]const u8, oar.Entry, table.string_context);
+
     ///
     /// Platform-agnostic mechanism for referencing files and directories on a [FileSystem].
     ///
@@ -447,23 +462,23 @@ pub const FileSystem = union(enum) {
                 .archive => |*archive| {
                     if (mode != .readonly) return error.ModeUnsupported;
 
-                    for (archive.entry_table) |_, index| {
-                        if (archive.entry_table[index].using == null) {
-                            const archive_path = path.buffer[0 .. path.length];
+                    for (archive.entry_table) |*entry| if (entry.using == null) {
+                        const entry_path = path.buffer[0 .. path.length];
+
+                        entry.* = .{
+                            .header = find_header: {
+                                if (archive.index_cache.lookup(entry_path)) |header|
+                                    break: find_header header.*;
 
-                            const entry_header = archive.index_cache.lookup(archive_path) orelse {
                                 const header = oar.Entry.find(archive.file_access,
-                                    archive_path) catch return error.FileNotFound;
+                                    entry_path) catch return error.FileNotFound;
 
-                                archive.index_cache.insert(archive_path, header) catch {
                                 // If caching fails... oh well...
-                                };
+                                archive.index_cache.insert(entry_path, header) catch {};
 
-                                break header;
-                            };
+                                break: find_header header;
+                            },
 
-                            archive.entry_table[index] = .{
-                                .header = entry_header,
                             .using = &archive.file_access,
                             .cursor = 0,
                         };
@@ -527,7 +542,7 @@ pub const FileSystem = union(enum) {
                         };
 
                         return FileAccess{
-                                .context = &archive.entry_table[index],
+                            .context = entry,
 
                             .implementation = &.{
                                 .close = Implementation.close,
@@ -538,8 +553,7 @@ pub const FileSystem = union(enum) {
                                 .seekToEnd = Implementation.seekToEnd,
                             },
                         };
-                        }
-                    }
+                    };
 
                     return error.OutOfFiles;
                 },
@@ -805,7 +819,7 @@ pub const RunError = error {
 /// Should an error from `run` occur, an `Error` is returned, otherwise a [RunError] is returned if
 /// the underlying runtime fails and is logged.
 ///
-pub fn runGraphics(comptime Error: anytype,
+pub fn runGraphics(allocator: std.mem.Allocator, comptime Error: anytype,
     comptime run: GraphicsRunner(Error)) (RunError || Error)!void {
 
     if (ext.SDL_Init(ext.SDL_INIT_EVERYTHING) != 0) {
@@ -841,14 +855,6 @@ pub fn runGraphics(comptime Error: anytype,
 
     defer ext.SDL_DestroyRenderer(renderer);
 
-    const user_path_prefix = ext.SDL_GetPrefPath("ona", "ona") orelse {
-        ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, "Failed to load user path");
-
-        return error.InitFailure;
-    };
-
-    defer ext.SDL_free(user_path_prefix);
-
     var cwd_file_system = FileSystem{.native =.{.path_prefix = "./"}};
 
     var data_archive_file_access = try (try cwd_file_system.
@@ -856,9 +862,7 @@ pub fn runGraphics(comptime Error: anytype,
 
     defer data_archive_file_access.close();
 
-    var app_context = AppContext.Implementation.init(data_archive_file_access,
-        user_path_prefix[0 .. std.mem.len(user_path_prefix)]) catch |err| {
-
+    var app_context = AppContext.Implementation.init(allocator, data_archive_file_access) catch |err| {
         ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, switch (err) {
             error.OutOfMemory => "Failed to allocate necessary memory",
             error.OutOfMutexes => "Failed to create file-system work lock",

src/table.zig

@@ -1,61 +1,119 @@
 const std = @import("std");
 
-pub fn Dynamic(comptime Key: type, comptime Value: type, comptime key_context: KeyContext(Key)) type {
+///
+/// Returns a hash-backed table type of `Value`s indexed by `Key` and using `key_context` as the key
+/// context.
+///
+pub fn Hashed(comptime Key: type, comptime Value: type,
+    comptime key_context: KeyContext(Key)) type {
+
+    const Allocator = std.mem.Allocator;
+
     return struct {
-        load_maximum: f32,
-        buckets_used: usize,
+        allocator: Allocator,
+        load_limit: f32,
         buckets: []Bucket,
+        filled: usize,
 
         ///
-        ///
+        /// A slot in the hash table.
         ///
         const Bucket = struct {
             maybe_entry: ?struct {
                 key: Key,
                 value: Value,
-            },
+            } = null,
 
-            maybe_next_index: ?usize,
+            maybe_next_index: ?usize = null,
         };
 
         ///
-        ///
+        /// Hash table type.
         ///
         const Self = @This();
 
         ///
+        /// Searches for `key` to delete it, returning the deleted value or `null` if no matching
+        /// key was found.
         ///
-        ///
-        pub fn delete(self: Self, key: Key) bool {
-            _ = key;
-            _ = self;
+        pub fn remove(self: Self, key: Key) ?Value {
+            var bucket = &(self.buckets[@mod(key_context.hash(key), self.buckets.len)]);
+
+            if (bucket.maybe_entry) |*entry| if (key_context.equals(entry.key, key)) {
+                defer entry.value = null;
+
+                self.filled -= 1;
+
+                return entry.value;
+            };
+
+            while (bucket.maybe_next_index) |index| {
+                bucket = &(self.buckets[index]);
+
+                if (bucket.maybe_entry) |*entry| if (key_context.equals(entry.key, key)) {
+                    defer entry.value = null;
+
+                    self.filled -= 1;
+
+                    return entry.value;
+                };
+            }
+
+            return null;
+        }
+
+        pub fn init(allocator: Allocator) Allocator.Error!Self {
+            return Self{
+                .buckets = try allocator.alloc(Bucket, 4),
+                .filled = 0,
+                .allocator = allocator,
+                .load_limit = 0.75,
+            };
         }
 
         ///
+        /// Attempts to insert the value at `key` to be `value` in `self`, returning an
+        /// [InsertError] if it fails.
         ///
-        ///
-        pub fn insert(self: Self, key: Key, value: Value) InsertError!void {
-            if ((@intToFloat(f32, self.buckets_used) / @intToFloat(
-                f32, self.buckets.len)) >= self.load_maximum) try self.rehash();
+        pub fn insert(self: *Self, key: Key, value: Value) InsertError!void {
+            if (self.loadFactor() >= self.load_limit) {
+                const old_buckets = self.buckets;
+
+                defer self.allocator.free(old_buckets);
+
+                self.buckets = try self.allocator.alloc(Bucket, old_buckets.len * 2);
+
+                for (old_buckets) |bucket, index| self.buckets[index] = bucket;
+            }
 
             var hash = @mod(key_context.hash(key), self.buckets.len);
 
             while (true) {
                 const bucket = &(self.buckets[hash]);
 
-                const entry = &(bucket.maybe_entry orelse {
+                if (key_context.equals((bucket.maybe_entry orelse {
                     bucket.maybe_entry = .{
                         .key = key,
                         .value = value
                     };
-                });
 
-                if (key_context.equals(entry.key, key)) return error.KeyExists;
+                    self.filled += 1;
 
-                hash = @mod(hashHash(hash), self.buckets.len);
+                    break;
+                }).key, key)) return error.KeyExists;
+
+                hash = @mod(hash + 1, self.buckets.len);
             }
         }
 
+        ///
+        /// Returns the current load factor of `self`, which is derived from the number of capacity
+        /// that has been filled.
+        ///
+        pub fn loadFactor(self: Self) f32 {
+            return @intToFloat(f32, self.filled) / @intToFloat(f32, self.buckets.len);
+        }
+
         ///
         /// Searches for a value indexed with `key` in `self`, returning it or `null` if no matching
         /// entry was found.
@@ -81,7 +139,7 @@ pub fn Dynamic(comptime Key: type, comptime Value: type, comptime key_context: K
 ///
 ///
 ///
-pub const InsertError = std.mem.Allocator || error {
+pub const InsertError = std.mem.Allocator.Error || error {
     KeyExists,
 };