std.rand: Refactor Random interface

These changes have been made to resolve issue ziglang#10037. The `Random`
interface was implemented in such a way that causes significant slowdown
when calling the `fill` function of the rng used.

The `Random` interface is no longer stored in a field of the rng, and is
instead returned by the child function `random()` of the rng. This
avoids the performance issues caused by the interface.

Author: ominitay

lib/std/atomic/queue.zig

@@ -242,10 +242,11 @@ test "std.atomic.Queue" {
 
 fn startPuts(ctx: *Context) u8 {
     var put_count: usize = puts_per_thread;
-    var r = std.rand.DefaultPrng.init(0xdeadbeef);
+    var prng = std.rand.DefaultPrng.init(0xdeadbeef);
+    const random = prng.random();
     while (put_count != 0) : (put_count -= 1) {
         std.time.sleep(1); // let the os scheduler be our fuzz
-        const x = @bitCast(i32, r.random.int(u32));
+        const x = @bitCast(i32, random.int(u32));
         const node = ctx.allocator.create(Queue(i32).Node) catch unreachable;
         node.* = .{
             .prev = undefined,

lib/std/atomic/stack.zig

@@ -147,10 +147,11 @@ test "std.atomic.stack" {
 
 fn startPuts(ctx: *Context) u8 {
     var put_count: usize = puts_per_thread;
-    var r = std.rand.DefaultPrng.init(0xdeadbeef);
+    var prng = std.rand.DefaultPrng.init(0xdeadbeef);
+    const random = prng.random();
     while (put_count != 0) : (put_count -= 1) {
         std.time.sleep(1); // let the os scheduler be our fuzz
-        const x = @bitCast(i32, r.random.int(u32));
+        const x = @bitCast(i32, random.int(u32));
         const node = ctx.allocator.create(Stack(i32).Node) catch unreachable;
         node.* = Stack(i32).Node{
             .next = undefined,

lib/std/crypto/benchmark.zig

@@ -11,6 +11,7 @@ const KiB = 1024;
 const MiB = 1024 * KiB;
 
 var prng = std.rand.DefaultPrng.init(0);
+const random = prng.random();
 
 const Crypto = struct {
     ty: type,
@@ -34,7 +35,7 @@ pub fn benchmarkHash(comptime Hash: anytype, comptime bytes: comptime_int) !u64
     var h = Hash.init(.{});
 
     var block: [Hash.digest_length]u8 = undefined;
-    prng.random.bytes(block[0..]);
+    random.bytes(block[0..]);
 
     var offset: usize = 0;
     var timer = try Timer.start();
@@ -66,11 +67,11 @@ const macs = [_]Crypto{
 
 pub fn benchmarkMac(comptime Mac: anytype, comptime bytes: comptime_int) !u64 {
     var in: [512 * KiB]u8 = undefined;
-    prng.random.bytes(in[0..]);
+    random.bytes(in[0..]);
 
     const key_length = if (Mac.key_length == 0) 32 else Mac.key_length;
     var key: [key_length]u8 = undefined;
-    prng.random.bytes(key[0..]);
+    random.bytes(key[0..]);
 
     var mac: [Mac.mac_length]u8 = undefined;
     var offset: usize = 0;
@@ -94,10 +95,10 @@ pub fn benchmarkKeyExchange(comptime DhKeyExchange: anytype, comptime exchange_c
     std.debug.assert(DhKeyExchange.shared_length >= DhKeyExchange.secret_length);
 
     var secret: [DhKeyExchange.shared_length]u8 = undefined;
-    prng.random.bytes(secret[0..]);
+    random.bytes(secret[0..]);
 
     var public: [DhKeyExchange.shared_length]u8 = undefined;
-    prng.random.bytes(public[0..]);
+    random.bytes(public[0..]);
 
     var timer = try Timer.start();
     const start = timer.lap();
@@ -211,15 +212,15 @@ const aeads = [_]Crypto{
 
 pub fn benchmarkAead(comptime Aead: anytype, comptime bytes: comptime_int) !u64 {
     var in: [512 * KiB]u8 = undefined;
-    prng.random.bytes(in[0..]);
+    random.bytes(in[0..]);
 
     var tag: [Aead.tag_length]u8 = undefined;
 
     var key: [Aead.key_length]u8 = undefined;
-    prng.random.bytes(key[0..]);
+    random.bytes(key[0..]);
 
     var nonce: [Aead.nonce_length]u8 = undefined;
-    prng.random.bytes(nonce[0..]);
+    random.bytes(nonce[0..]);
 
     var offset: usize = 0;
     var timer = try Timer.start();
@@ -244,7 +245,7 @@ const aes = [_]Crypto{
 
 pub fn benchmarkAes(comptime Aes: anytype, comptime count: comptime_int) !u64 {
     var key: [Aes.key_bits / 8]u8 = undefined;
-    prng.random.bytes(key[0..]);
+    random.bytes(key[0..]);
     const ctx = Aes.initEnc(key);
 
     var in = [_]u8{0} ** 16;
@@ -273,7 +274,7 @@ const aes8 = [_]Crypto{
 
 pub fn benchmarkAes8(comptime Aes: anytype, comptime count: comptime_int) !u64 {
     var key: [Aes.key_bits / 8]u8 = undefined;
-    prng.random.bytes(key[0..]);
+    random.bytes(key[0..]);
     const ctx = Aes.initEnc(key);
 
     var in = [_]u8{0} ** (8 * 16);

lib/std/crypto/tlcsprng.zig

@@ -11,7 +11,10 @@ const os = std.os;
 
 /// We use this as a layer of indirection because global const pointers cannot
 /// point to thread-local variables.
-pub var interface = std.rand.Random{ .fillFn = tlsCsprngFill };
+pub const interface = std.rand.Random{
+    .ptr = undefined,
+    .fillFn = tlsCsprngFill,
+};
 
 const os_has_fork = switch (builtin.os.tag) {
     .dragonfly,
@@ -55,7 +58,7 @@ var install_atfork_handler = std.once(struct {
 
 threadlocal var wipe_mem: []align(mem.page_size) u8 = &[_]u8{};
 
-fn tlsCsprngFill(_: *const std.rand.Random, buffer: []u8) void {
+fn tlsCsprngFill(_: *c_void, buffer: []u8) void {
     if (builtin.link_libc and @hasDecl(std.c, "arc4random_buf")) {
         // arc4random is already a thread-local CSPRNG.
         return std.c.arc4random_buf(buffer.ptr, buffer.len);

lib/std/hash/benchmark.zig

@@ -11,6 +11,7 @@ const MiB = 1024 * KiB;
 const GiB = 1024 * MiB;
 
 var prng = std.rand.DefaultPrng.init(0);
+const random = prng.random();
 
 const Hash = struct {
     ty: type,
@@ -88,7 +89,7 @@ pub fn benchmarkHash(comptime H: anytype, bytes: usize) !Result {
     };
 
     var block: [block_size]u8 = undefined;
-    prng.random.bytes(block[0..]);
+    random.bytes(block[0..]);
 
     var offset: usize = 0;
     var timer = try Timer.start();
@@ -110,7 +111,7 @@ pub fn benchmarkHash(comptime H: anytype, bytes: usize) !Result {
 pub fn benchmarkHashSmallKeys(comptime H: anytype, key_size: usize, bytes: usize) !Result {
     const key_count = bytes / key_size;
     var block: [block_size]u8 = undefined;
-    prng.random.bytes(block[0..]);
+    random.bytes(block[0..]);
 
     var i: usize = 0;
     var timer = try Timer.start();

lib/std/hash_map.zig

@@ -1795,10 +1795,11 @@ test "std.hash_map put and remove loop in random order" {
     while (i < size) : (i += 1) {
         try keys.append(i);
     }
-    var rng = std.rand.DefaultPrng.init(0);
+    var prng = std.rand.DefaultPrng.init(0);
+    const random = prng.random();
 
     while (i < iterations) : (i += 1) {
-        std.rand.Random.shuffle(&rng.random, u32, keys.items);
+        random.shuffle(u32, keys.items);
 
         for (keys.items) |key| {
             try map.put(key, key);
@@ -1826,14 +1827,15 @@ test "std.hash_map remove one million elements in random order" {
         keys.append(i) catch unreachable;
     }
 
-    var rng = std.rand.DefaultPrng.init(0);
-    std.rand.Random.shuffle(&rng.random, u32, keys.items);
+    var prng = std.rand.DefaultPrng.init(0);
+    const random = prng.random();
+    random.shuffle(u32, keys.items);
 
     for (keys.items) |key| {
         map.put(key, key) catch unreachable;
     }
 
-    std.rand.Random.shuffle(&rng.random, u32, keys.items);
+    random.shuffle(u32, keys.items);
     i = 0;
     while (i < n) : (i += 1) {
         const key = keys.items[i];

lib/std/io/test.zig

@@ -20,7 +20,8 @@ test "write a file, read it, then delete it" {
 
     var data: [1024]u8 = undefined;
     var prng = DefaultPrng.init(1234);
-    prng.random.bytes(data[0..]);
+    const random = prng.random();
+    random.bytes(data[0..]);
     const tmp_file_name = "temp_test_file.txt";
     {
         var file = try tmp.dir.createFile(tmp_file_name, .{});

lib/std/math/big/rational.zig

@@ -589,9 +589,10 @@ test "big.rational set/to Float round-trip" {
     var a = try Rational.init(testing.allocator);
     defer a.deinit();
     var prng = std.rand.DefaultPrng.init(0x5EED);
+    const random = prng.random();
     var i: usize = 0;
     while (i < 512) : (i += 1) {
-        const r = prng.random.float(f64);
+        const r = random.float(f64);
         try a.setFloat(f64, r);
         try testing.expect((try a.toFloat(f64)) == r);
     }

lib/std/priority_dequeue.zig

@@ -850,17 +850,18 @@ test "std.PriorityDequeue: shrinkAndFree" {
 
 test "std.PriorityDequeue: fuzz testing min" {
     var prng = std.rand.DefaultPrng.init(0x12345678);
+    const random = prng.random();
 
     const test_case_count = 100;
     const queue_size = 1_000;
 
     var i: usize = 0;
     while (i < test_case_count) : (i += 1) {
-        try fuzzTestMin(&prng.random, queue_size);
+        try fuzzTestMin(random, queue_size);
     }
 }
 
-fn fuzzTestMin(rng: *std.rand.Random, comptime queue_size: usize) !void {
+fn fuzzTestMin(rng: std.rand.Random, comptime queue_size: usize) !void {
     const allocator = testing.allocator;
     const items = try generateRandomSlice(allocator, rng, queue_size);
 
@@ -878,17 +879,18 @@ fn fuzzTestMin(rng: *std.rand.Random, comptime queue_size: usize) !void {
 
 test "std.PriorityDequeue: fuzz testing max" {
     var prng = std.rand.DefaultPrng.init(0x87654321);
+    const random = prng.random();
 
     const test_case_count = 100;
     const queue_size = 1_000;
 
     var i: usize = 0;
     while (i < test_case_count) : (i += 1) {
-        try fuzzTestMax(&prng.random, queue_size);
+        try fuzzTestMax(random, queue_size);
     }
 }
 
-fn fuzzTestMax(rng: *std.rand.Random, queue_size: usize) !void {
+fn fuzzTestMax(rng: std.rand.Random, queue_size: usize) !void {
     const allocator = testing.allocator;
     const items = try generateRandomSlice(allocator, rng, queue_size);
 
@@ -906,17 +908,18 @@ fn fuzzTestMax(rng: *std.rand.Random, queue_size: usize) !void {
 
 test "std.PriorityDequeue: fuzz testing min and max" {
     var prng = std.rand.DefaultPrng.init(0x87654321);
+    const random = prng.random();
 
     const test_case_count = 100;
     const queue_size = 1_000;
 
     var i: usize = 0;
     while (i < test_case_count) : (i += 1) {
-        try fuzzTestMinMax(&prng.random, queue_size);
+        try fuzzTestMinMax(random, queue_size);
     }
 }
 
-fn fuzzTestMinMax(rng: *std.rand.Random, queue_size: usize) !void {
+fn fuzzTestMinMax(rng: std.rand.Random, queue_size: usize) !void {
     const allocator = testing.allocator;
     const items = try generateRandomSlice(allocator, rng, queue_size);
 
@@ -943,7 +946,7 @@ fn fuzzTestMinMax(rng: *std.rand.Random, queue_size: usize) !void {
     }
 }
 
-fn generateRandomSlice(allocator: *std.mem.Allocator, rng: *std.rand.Random, size: usize) ![]u32 {
+fn generateRandomSlice(allocator: *std.mem.Allocator, rng: std.rand.Random, size: usize) ![]u32 {
     var array = std.ArrayList(u32).init(allocator);
     try array.ensureTotalCapacity(size);