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general_purpose_allocator.zig
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general_purpose_allocator.zig
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//! # General Purpose Allocator
//!
//! ## Design Priorities
//!
//! ### `OptimizationMode.debug` and `OptimizationMode.release_safe`:
//!
//! * Detect double free, and emit stack trace of:
//! - Where it was first allocated
//! - Where it was freed the first time
//! - Where it was freed the second time
//!
//! * Detect leaks and emit stack trace of:
//! - Where it was allocated
//!
//! * When a page of memory is no longer needed, give it back to resident memory
//! as soon as possible, so that it causes page faults when used.
//!
//! * Do not re-use memory slots, so that memory safety is upheld. For small
//! allocations, this is handled here; for larger ones it is handled in the
//! backing allocator (by default `std.heap.page_allocator`).
//!
//! * Make pointer math errors unlikely to harm memory from
//! unrelated allocations.
//!
//! * It's OK for these mechanisms to cost some extra overhead bytes.
//!
//! * It's OK for performance cost for these mechanisms.
//!
//! * Rogue memory writes should not harm the allocator's state.
//!
//! * Cross platform. Operates based on a backing allocator which makes it work
//! everywhere, even freestanding.
//!
//! * Compile-time configuration.
//!
//! ### `OptimizationMode.release_fast` (note: not much work has gone into this use case yet):
//!
//! * Low fragmentation is primary concern
//! * Performance of worst-case latency is secondary concern
//! * Performance of average-case latency is next
//! * Finally, having freed memory unmapped, and pointer math errors unlikely to
//! harm memory from unrelated allocations are nice-to-haves.
//!
//! ### `OptimizationMode.release_small` (note: not much work has gone into this use case yet):
//!
//! * Small binary code size of the executable is the primary concern.
//! * Next, defer to the `.release_fast` priority list.
//!
//! ## Basic Design:
//!
//! Small allocations are divided into buckets:
//!
//! ```
//! index obj_size
//! 0 1
//! 1 2
//! 2 4
//! 3 8
//! 4 16
//! 5 32
//! 6 64
//! 7 128
//! 8 256
//! 9 512
//! 10 1024
//! 11 2048
//! ```
//!
//! The main allocator state has an array of all the "current" buckets for each
//! size class. Each slot in the array can be null, meaning the bucket for that
//! size class is not allocated. When the first object is allocated for a given
//! size class, it allocates 1 page of memory from the OS. This page is
//! divided into "slots" - one per allocated object. Along with the page of memory
//! for object slots, as many pages as necessary are allocated to store the
//! BucketHeader, followed by "used bits", and two stack traces for each slot
//! (allocation trace and free trace).
//!
//! The "used bits" are 1 bit per slot representing whether the slot is used.
//! Allocations use the data to iterate to find a free slot. Frees assert that the
//! corresponding bit is 1 and set it to 0.
//!
//! Buckets have prev and next pointers. When there is only one bucket for a given
//! size class, both prev and next point to itself. When all slots of a bucket are
//! used, a new bucket is allocated, and enters the doubly linked list. The main
//! allocator state tracks the "current" bucket for each size class. Leak detection
//! currently only checks the current bucket.
//!
//! Resizing detects if the size class is unchanged or smaller, in which case the same
//! pointer is returned unmodified. If a larger size class is required,
//! `error.OutOfMemory` is returned.
//!
//! Large objects are allocated directly using the backing allocator and their metadata is stored
//! in a `std.HashMap` using the backing allocator.
const std = @import("std");
const builtin = @import("builtin");
const log = std.log.scoped(.gpa);
const math = std.math;
const assert = std.debug.assert;
const mem = std.mem;
const Allocator = std.mem.Allocator;
const page_size = std.mem.page_size;
const StackTrace = std.builtin.StackTrace;
/// Integer type for pointing to slots in a small allocation
const SlotIndex = std.meta.Int(.unsigned, math.log2(page_size) + 1);
const default_test_stack_trace_frames: usize = if (builtin.is_test) 8 else 4;
const default_sys_stack_trace_frames: usize = if (std.debug.sys_can_stack_trace) default_test_stack_trace_frames else 0;
const default_stack_trace_frames: usize = switch (builtin.mode) {
.Debug => default_sys_stack_trace_frames,
else => 0,
};
pub const Config = struct {
/// Number of stack frames to capture.
stack_trace_frames: usize = default_stack_trace_frames,
/// If true, the allocator will have two fields:
/// * `total_requested_bytes` which tracks the total allocated bytes of memory requested.
/// * `requested_memory_limit` which causes allocations to return `error.OutOfMemory`
/// when the `total_requested_bytes` exceeds this limit.
/// If false, these fields will be `void`.
enable_memory_limit: bool = false,
/// Whether to enable safety checks.
safety: bool = std.debug.runtime_safety,
/// Whether the allocator may be used simultaneously from multiple threads.
thread_safe: bool = !builtin.single_threaded,
/// What type of mutex you'd like to use, for thread safety.
/// when specified, the mutex type must have the same shape as `std.Thread.Mutex` and
/// `DummyMutex`, and have no required fields. Specifying this field causes
/// the `thread_safe` field to be ignored.
///
/// when null (default):
/// * the mutex type defaults to `std.Thread.Mutex` when thread_safe is enabled.
/// * the mutex type defaults to `DummyMutex` otherwise.
MutexType: ?type = null,
/// This is a temporary debugging trick you can use to turn segfaults into more helpful
/// logged error messages with stack trace details. The downside is that every allocation
/// will be leaked, unless used with retain_metadata!
never_unmap: bool = false,
/// This is a temporary debugging aid that retains metadata about allocations indefinitely.
/// This allows a greater range of double frees to be reported. All metadata is freed when
/// deinit is called. When used with never_unmap, deliberately leaked memory is also freed
/// during deinit. Currently should be used with never_unmap to avoid segfaults.
/// TODO https://github.com/ziglang/zig/issues/4298 will allow use without never_unmap
retain_metadata: bool = false,
/// Enables emitting info messages with the size and address of every allocation.
verbose_log: bool = false,
};
pub const Check = enum { ok, leak };
pub fn GeneralPurposeAllocator(comptime config: Config) type {
return struct {
backing_allocator: Allocator = std.heap.page_allocator,
buckets: [small_bucket_count]?*BucketHeader = [1]?*BucketHeader{null} ** small_bucket_count,
large_allocations: LargeAllocTable = .{},
small_allocations: if (config.safety) SmallAllocTable else void = if (config.safety) .{} else {},
empty_buckets: if (config.retain_metadata) ?*BucketHeader else void =
if (config.retain_metadata) null else {},
total_requested_bytes: @TypeOf(total_requested_bytes_init) = total_requested_bytes_init,
requested_memory_limit: @TypeOf(requested_memory_limit_init) = requested_memory_limit_init,
mutex: @TypeOf(mutex_init) = mutex_init,
const Self = @This();
const total_requested_bytes_init = if (config.enable_memory_limit) @as(usize, 0) else {};
const requested_memory_limit_init = if (config.enable_memory_limit) @as(usize, math.maxInt(usize)) else {};
const mutex_init = if (config.MutexType) |T|
T{}
else if (config.thread_safe)
std.Thread.Mutex{}
else
DummyMutex{};
const DummyMutex = struct {
fn lock(_: *DummyMutex) void {}
fn unlock(_: *DummyMutex) void {}
};
const stack_n = config.stack_trace_frames;
const one_trace_size = @sizeOf(usize) * stack_n;
const traces_per_slot = 2;
pub const Error = mem.Allocator.Error;
const small_bucket_count = math.log2(page_size);
const largest_bucket_object_size = 1 << (small_bucket_count - 1);
const SmallAlloc = struct {
requested_size: usize,
log2_ptr_align: u8,
};
const LargeAlloc = struct {
bytes: []u8,
requested_size: if (config.enable_memory_limit) usize else void,
stack_addresses: [trace_n][stack_n]usize,
freed: if (config.retain_metadata) bool else void,
log2_ptr_align: if (config.never_unmap and config.retain_metadata) u8 else void,
const trace_n = if (config.retain_metadata) traces_per_slot else 1;
fn dumpStackTrace(self: *LargeAlloc, trace_kind: TraceKind) void {
std.debug.dumpStackTrace(self.getStackTrace(trace_kind));
}
fn getStackTrace(self: *LargeAlloc, trace_kind: TraceKind) std.builtin.StackTrace {
assert(@intFromEnum(trace_kind) < trace_n);
const stack_addresses = &self.stack_addresses[@intFromEnum(trace_kind)];
var len: usize = 0;
while (len < stack_n and stack_addresses[len] != 0) {
len += 1;
}
return .{
.instruction_addresses = stack_addresses,
.index = len,
};
}
fn captureStackTrace(self: *LargeAlloc, ret_addr: usize, trace_kind: TraceKind) void {
assert(@intFromEnum(trace_kind) < trace_n);
const stack_addresses = &self.stack_addresses[@intFromEnum(trace_kind)];
collectStackTrace(ret_addr, stack_addresses);
}
};
const LargeAllocTable = std.AutoHashMapUnmanaged(usize, LargeAlloc);
const SmallAllocTable = std.AutoHashMapUnmanaged(usize, SmallAlloc);
// Bucket: In memory, in order:
// * BucketHeader
// * bucket_used_bits: [N]u8, // 1 bit for every slot; 1 byte for every 8 slots
// * stack_trace_addresses: [N]usize, // traces_per_slot for every allocation
const BucketHeader = struct {
prev: *BucketHeader,
next: *BucketHeader,
page: [*]align(page_size) u8,
alloc_cursor: SlotIndex,
used_count: SlotIndex,
fn usedBits(bucket: *BucketHeader, index: usize) *u8 {
return @as(*u8, @ptrFromInt(@intFromPtr(bucket) + @sizeOf(BucketHeader) + index));
}
fn stackTracePtr(
bucket: *BucketHeader,
size_class: usize,
slot_index: SlotIndex,
trace_kind: TraceKind,
) *[stack_n]usize {
const start_ptr = @as([*]u8, @ptrCast(bucket)) + bucketStackFramesStart(size_class);
const addr = start_ptr + one_trace_size * traces_per_slot * slot_index +
@intFromEnum(trace_kind) * @as(usize, one_trace_size);
return @ptrCast(@alignCast(addr));
}
fn captureStackTrace(
bucket: *BucketHeader,
ret_addr: usize,
size_class: usize,
slot_index: SlotIndex,
trace_kind: TraceKind,
) void {
// Initialize them to 0. When determining the count we must look
// for non zero addresses.
const stack_addresses = bucket.stackTracePtr(size_class, slot_index, trace_kind);
collectStackTrace(ret_addr, stack_addresses);
}
};
pub fn allocator(self: *Self) Allocator {
return .{
.ptr = self,
.vtable = &.{
.alloc = alloc,
.resize = resize,
.free = free,
},
};
}
fn bucketStackTrace(
bucket: *BucketHeader,
size_class: usize,
slot_index: SlotIndex,
trace_kind: TraceKind,
) StackTrace {
const stack_addresses = bucket.stackTracePtr(size_class, slot_index, trace_kind);
var len: usize = 0;
while (len < stack_n and stack_addresses[len] != 0) {
len += 1;
}
return StackTrace{
.instruction_addresses = stack_addresses,
.index = len,
};
}
fn bucketStackFramesStart(size_class: usize) usize {
return mem.alignForward(
usize,
@sizeOf(BucketHeader) + usedBitsCount(size_class),
@alignOf(usize),
);
}
fn bucketSize(size_class: usize) usize {
const slot_count = @divExact(page_size, size_class);
return bucketStackFramesStart(size_class) + one_trace_size * traces_per_slot * slot_count;
}
fn usedBitsCount(size_class: usize) usize {
const slot_count = @divExact(page_size, size_class);
if (slot_count < 8) return 1;
return @divExact(slot_count, 8);
}
fn detectLeaksInBucket(
bucket: *BucketHeader,
size_class: usize,
used_bits_count: usize,
) bool {
var leaks = false;
var used_bits_byte: usize = 0;
while (used_bits_byte < used_bits_count) : (used_bits_byte += 1) {
const used_byte = bucket.usedBits(used_bits_byte).*;
if (used_byte != 0) {
var bit_index: u3 = 0;
while (true) : (bit_index += 1) {
const is_used = @as(u1, @truncate(used_byte >> bit_index)) != 0;
if (is_used) {
const slot_index = @as(SlotIndex, @intCast(used_bits_byte * 8 + bit_index));
const stack_trace = bucketStackTrace(bucket, size_class, slot_index, .alloc);
const addr = bucket.page + slot_index * size_class;
log.err("memory address 0x{x} leaked: {}", .{
@intFromPtr(addr), stack_trace,
});
leaks = true;
}
if (bit_index == math.maxInt(u3))
break;
}
}
}
return leaks;
}
/// Emits log messages for leaks and then returns whether there were any leaks.
pub fn detectLeaks(self: *Self) bool {
var leaks = false;
for (self.buckets, 0..) |optional_bucket, bucket_i| {
const first_bucket = optional_bucket orelse continue;
const size_class = @as(usize, 1) << @as(math.Log2Int(usize), @intCast(bucket_i));
const used_bits_count = usedBitsCount(size_class);
var bucket = first_bucket;
while (true) {
leaks = detectLeaksInBucket(bucket, size_class, used_bits_count) or leaks;
bucket = bucket.next;
if (bucket == first_bucket)
break;
}
}
var it = self.large_allocations.valueIterator();
while (it.next()) |large_alloc| {
if (config.retain_metadata and large_alloc.freed) continue;
const stack_trace = large_alloc.getStackTrace(.alloc);
log.err("memory address 0x{x} leaked: {}", .{
@intFromPtr(large_alloc.bytes.ptr), stack_trace,
});
leaks = true;
}
return leaks;
}
fn freeBucket(self: *Self, bucket: *BucketHeader, size_class: usize) void {
const bucket_size = bucketSize(size_class);
const bucket_slice = @as([*]align(@alignOf(BucketHeader)) u8, @ptrCast(bucket))[0..bucket_size];
self.backing_allocator.free(bucket_slice);
}
fn freeRetainedMetadata(self: *Self) void {
if (config.retain_metadata) {
if (config.never_unmap) {
// free large allocations that were intentionally leaked by never_unmap
var it = self.large_allocations.iterator();
while (it.next()) |large| {
if (large.value_ptr.freed) {
self.backing_allocator.rawFree(large.value_ptr.bytes, large.value_ptr.log2_ptr_align, @returnAddress());
}
}
}
// free retained metadata for small allocations
if (self.empty_buckets) |first_bucket| {
var bucket = first_bucket;
while (true) {
const prev = bucket.prev;
if (config.never_unmap) {
// free page that was intentionally leaked by never_unmap
self.backing_allocator.free(bucket.page[0..page_size]);
}
// alloc_cursor was set to slot count when bucket added to empty_buckets
self.freeBucket(bucket, @divExact(page_size, bucket.alloc_cursor));
bucket = prev;
if (bucket == first_bucket)
break;
}
self.empty_buckets = null;
}
}
}
pub usingnamespace if (config.retain_metadata) struct {
pub fn flushRetainedMetadata(self: *Self) void {
self.freeRetainedMetadata();
// also remove entries from large_allocations
var it = self.large_allocations.iterator();
while (it.next()) |large| {
if (large.value_ptr.freed) {
_ = self.large_allocations.remove(@intFromPtr(large.value_ptr.bytes.ptr));
}
}
}
} else struct {};
/// Returns `Check.leak` if there were leaks; `Check.ok` otherwise.
pub fn deinit(self: *Self) Check {
const leaks = if (config.safety) self.detectLeaks() else false;
if (config.retain_metadata) {
self.freeRetainedMetadata();
}
self.large_allocations.deinit(self.backing_allocator);
if (config.safety) {
self.small_allocations.deinit(self.backing_allocator);
}
self.* = undefined;
return @as(Check, @enumFromInt(@intFromBool(leaks)));
}
fn collectStackTrace(first_trace_addr: usize, addresses: *[stack_n]usize) void {
if (stack_n == 0) return;
@memset(addresses, 0);
var stack_trace = StackTrace{
.instruction_addresses = addresses,
.index = 0,
};
std.debug.captureStackTrace(first_trace_addr, &stack_trace);
}
fn reportDoubleFree(ret_addr: usize, alloc_stack_trace: StackTrace, free_stack_trace: StackTrace) void {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var second_free_stack_trace = StackTrace{
.instruction_addresses = &addresses,
.index = 0,
};
std.debug.captureStackTrace(ret_addr, &second_free_stack_trace);
log.err("Double free detected. Allocation: {} First free: {} Second free: {}", .{
alloc_stack_trace, free_stack_trace, second_free_stack_trace,
});
}
fn allocSlot(self: *Self, size_class: usize, trace_addr: usize) Error![*]u8 {
const bucket_index = math.log2(size_class);
const first_bucket = self.buckets[bucket_index] orelse try self.createBucket(
size_class,
bucket_index,
);
var bucket = first_bucket;
const slot_count = @divExact(page_size, size_class);
while (bucket.alloc_cursor == slot_count) {
const prev_bucket = bucket;
bucket = prev_bucket.next;
if (bucket == first_bucket) {
// make a new one
bucket = try self.createBucket(size_class, bucket_index);
bucket.prev = prev_bucket;
bucket.next = prev_bucket.next;
prev_bucket.next = bucket;
bucket.next.prev = bucket;
}
}
// change the allocator's current bucket to be this one
self.buckets[bucket_index] = bucket;
const slot_index = bucket.alloc_cursor;
bucket.alloc_cursor += 1;
var used_bits_byte = bucket.usedBits(slot_index / 8);
const used_bit_index: u3 = @as(u3, @intCast(slot_index % 8)); // TODO cast should be unnecessary
used_bits_byte.* |= (@as(u8, 1) << used_bit_index);
bucket.used_count += 1;
bucket.captureStackTrace(trace_addr, size_class, slot_index, .alloc);
return bucket.page + slot_index * size_class;
}
fn searchBucket(
bucket_list: ?*BucketHeader,
addr: usize,
) ?*BucketHeader {
const first_bucket = bucket_list orelse return null;
var bucket = first_bucket;
while (true) {
const in_bucket_range = (addr >= @intFromPtr(bucket.page) and
addr < @intFromPtr(bucket.page) + page_size);
if (in_bucket_range) return bucket;
bucket = bucket.prev;
if (bucket == first_bucket) {
return null;
}
}
}
/// This function assumes the object is in the large object storage regardless
/// of the parameters.
fn resizeLarge(
self: *Self,
old_mem: []u8,
log2_old_align: u8,
new_size: usize,
ret_addr: usize,
) bool {
const entry = self.large_allocations.getEntry(@intFromPtr(old_mem.ptr)) orelse {
if (config.safety) {
@panic("Invalid free");
} else {
unreachable;
}
};
if (config.retain_metadata and entry.value_ptr.freed) {
if (config.safety) {
reportDoubleFree(ret_addr, entry.value_ptr.getStackTrace(.alloc), entry.value_ptr.getStackTrace(.free));
@panic("Unrecoverable double free");
} else {
unreachable;
}
}
if (config.safety and old_mem.len != entry.value_ptr.bytes.len) {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var free_stack_trace = StackTrace{
.instruction_addresses = &addresses,
.index = 0,
};
std.debug.captureStackTrace(ret_addr, &free_stack_trace);
log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {} Free: {}", .{
entry.value_ptr.bytes.len,
old_mem.len,
entry.value_ptr.getStackTrace(.alloc),
free_stack_trace,
});
}
// Do memory limit accounting with requested sizes rather than what
// backing_allocator returns because if we want to return
// error.OutOfMemory, we have to leave allocation untouched, and
// that is impossible to guarantee after calling
// backing_allocator.rawResize.
const prev_req_bytes = self.total_requested_bytes;
if (config.enable_memory_limit) {
const new_req_bytes = prev_req_bytes + new_size - entry.value_ptr.requested_size;
if (new_req_bytes > prev_req_bytes and new_req_bytes > self.requested_memory_limit) {
return false;
}
self.total_requested_bytes = new_req_bytes;
}
if (!self.backing_allocator.rawResize(old_mem, log2_old_align, new_size, ret_addr)) {
if (config.enable_memory_limit) {
self.total_requested_bytes = prev_req_bytes;
}
return false;
}
if (config.enable_memory_limit) {
entry.value_ptr.requested_size = new_size;
}
if (config.verbose_log) {
log.info("large resize {d} bytes at {*} to {d}", .{
old_mem.len, old_mem.ptr, new_size,
});
}
entry.value_ptr.bytes = old_mem.ptr[0..new_size];
entry.value_ptr.captureStackTrace(ret_addr, .alloc);
return true;
}
/// This function assumes the object is in the large object storage regardless
/// of the parameters.
fn freeLarge(
self: *Self,
old_mem: []u8,
log2_old_align: u8,
ret_addr: usize,
) void {
const entry = self.large_allocations.getEntry(@intFromPtr(old_mem.ptr)) orelse {
if (config.safety) {
@panic("Invalid free");
} else {
unreachable;
}
};
if (config.retain_metadata and entry.value_ptr.freed) {
if (config.safety) {
reportDoubleFree(ret_addr, entry.value_ptr.getStackTrace(.alloc), entry.value_ptr.getStackTrace(.free));
return;
} else {
unreachable;
}
}
if (config.safety and old_mem.len != entry.value_ptr.bytes.len) {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var free_stack_trace = StackTrace{
.instruction_addresses = &addresses,
.index = 0,
};
std.debug.captureStackTrace(ret_addr, &free_stack_trace);
log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {} Free: {}", .{
entry.value_ptr.bytes.len,
old_mem.len,
entry.value_ptr.getStackTrace(.alloc),
free_stack_trace,
});
}
if (!config.never_unmap) {
self.backing_allocator.rawFree(old_mem, log2_old_align, ret_addr);
}
if (config.enable_memory_limit) {
self.total_requested_bytes -= entry.value_ptr.requested_size;
}
if (config.verbose_log) {
log.info("large free {d} bytes at {*}", .{ old_mem.len, old_mem.ptr });
}
if (!config.retain_metadata) {
assert(self.large_allocations.remove(@intFromPtr(old_mem.ptr)));
} else {
entry.value_ptr.freed = true;
entry.value_ptr.captureStackTrace(ret_addr, .free);
}
}
pub fn setRequestedMemoryLimit(self: *Self, limit: usize) void {
self.requested_memory_limit = limit;
}
fn resize(
ctx: *anyopaque,
old_mem: []u8,
log2_old_align_u8: u8,
new_size: usize,
ret_addr: usize,
) bool {
const self: *Self = @ptrCast(@alignCast(ctx));
const log2_old_align = @as(Allocator.Log2Align, @intCast(log2_old_align_u8));
self.mutex.lock();
defer self.mutex.unlock();
assert(old_mem.len != 0);
const aligned_size = @max(old_mem.len, @as(usize, 1) << log2_old_align);
if (aligned_size > largest_bucket_object_size) {
return self.resizeLarge(old_mem, log2_old_align, new_size, ret_addr);
}
const size_class_hint = math.ceilPowerOfTwoAssert(usize, aligned_size);
var bucket_index = math.log2(size_class_hint);
var size_class: usize = size_class_hint;
const bucket = while (bucket_index < small_bucket_count) : (bucket_index += 1) {
if (searchBucket(self.buckets[bucket_index], @intFromPtr(old_mem.ptr))) |bucket| {
// move bucket to head of list to optimize search for nearby allocations
self.buckets[bucket_index] = bucket;
break bucket;
}
size_class *= 2;
} else blk: {
if (config.retain_metadata) {
if (!self.large_allocations.contains(@intFromPtr(old_mem.ptr))) {
// object not in active buckets or a large allocation, so search empty buckets
if (searchBucket(self.empty_buckets, @intFromPtr(old_mem.ptr))) |bucket| {
// bucket is empty so is_used below will always be false and we exit there
break :blk bucket;
} else {
@panic("Invalid free");
}
}
}
return self.resizeLarge(old_mem, log2_old_align, new_size, ret_addr);
};
const byte_offset = @intFromPtr(old_mem.ptr) - @intFromPtr(bucket.page);
const slot_index = @as(SlotIndex, @intCast(byte_offset / size_class));
const used_byte_index = slot_index / 8;
const used_bit_index = @as(u3, @intCast(slot_index % 8));
const used_byte = bucket.usedBits(used_byte_index);
const is_used = @as(u1, @truncate(used_byte.* >> used_bit_index)) != 0;
if (!is_used) {
if (config.safety) {
reportDoubleFree(ret_addr, bucketStackTrace(bucket, size_class, slot_index, .alloc), bucketStackTrace(bucket, size_class, slot_index, .free));
@panic("Unrecoverable double free");
} else {
unreachable;
}
}
// Definitely an in-use small alloc now.
if (config.safety) {
const entry = self.small_allocations.getEntry(@intFromPtr(old_mem.ptr)) orelse
@panic("Invalid free");
if (old_mem.len != entry.value_ptr.requested_size or log2_old_align != entry.value_ptr.log2_ptr_align) {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var free_stack_trace = StackTrace{
.instruction_addresses = &addresses,
.index = 0,
};
std.debug.captureStackTrace(ret_addr, &free_stack_trace);
if (old_mem.len != entry.value_ptr.requested_size) {
log.err("Allocation size {d} bytes does not match resize size {d}. Allocation: {} Resize: {}", .{
entry.value_ptr.requested_size,
old_mem.len,
bucketStackTrace(bucket, size_class, slot_index, .alloc),
free_stack_trace,
});
}
if (log2_old_align != entry.value_ptr.log2_ptr_align) {
log.err("Allocation alignment {d} does not match resize alignment {d}. Allocation: {} Resize: {}", .{
@as(usize, 1) << @as(math.Log2Int(usize), @intCast(entry.value_ptr.log2_ptr_align)),
@as(usize, 1) << @as(math.Log2Int(usize), @intCast(log2_old_align)),
bucketStackTrace(bucket, size_class, slot_index, .alloc),
free_stack_trace,
});
}
}
}
const prev_req_bytes = self.total_requested_bytes;
if (config.enable_memory_limit) {
const new_req_bytes = prev_req_bytes + new_size - old_mem.len;
if (new_req_bytes > prev_req_bytes and new_req_bytes > self.requested_memory_limit) {
return false;
}
self.total_requested_bytes = new_req_bytes;
}
const new_aligned_size = @max(new_size, @as(usize, 1) << log2_old_align);
const new_size_class = math.ceilPowerOfTwoAssert(usize, new_aligned_size);
if (new_size_class <= size_class) {
if (old_mem.len > new_size) {
@memset(old_mem[new_size..], undefined);
}
if (config.verbose_log) {
log.info("small resize {d} bytes at {*} to {d}", .{
old_mem.len, old_mem.ptr, new_size,
});
}
if (config.safety) {
const entry = self.small_allocations.getEntry(@intFromPtr(old_mem.ptr)).?;
entry.value_ptr.requested_size = new_size;
}
return true;
}
if (config.enable_memory_limit) {
self.total_requested_bytes = prev_req_bytes;
}
return false;
}
fn free(
ctx: *anyopaque,
old_mem: []u8,
log2_old_align_u8: u8,
ret_addr: usize,
) void {
const self: *Self = @ptrCast(@alignCast(ctx));
const log2_old_align = @as(Allocator.Log2Align, @intCast(log2_old_align_u8));
self.mutex.lock();
defer self.mutex.unlock();
assert(old_mem.len != 0);
const aligned_size = @max(old_mem.len, @as(usize, 1) << log2_old_align);
if (aligned_size > largest_bucket_object_size) {
self.freeLarge(old_mem, log2_old_align, ret_addr);
return;
}
const size_class_hint = math.ceilPowerOfTwoAssert(usize, aligned_size);
var bucket_index = math.log2(size_class_hint);
var size_class: usize = size_class_hint;
const bucket = while (bucket_index < small_bucket_count) : (bucket_index += 1) {
if (searchBucket(self.buckets[bucket_index], @intFromPtr(old_mem.ptr))) |bucket| {
// move bucket to head of list to optimize search for nearby allocations
self.buckets[bucket_index] = bucket;
break bucket;
}
size_class *= 2;
} else blk: {
if (config.retain_metadata) {
if (!self.large_allocations.contains(@intFromPtr(old_mem.ptr))) {
// object not in active buckets or a large allocation, so search empty buckets
if (searchBucket(self.empty_buckets, @intFromPtr(old_mem.ptr))) |bucket| {
// bucket is empty so is_used below will always be false and we exit there
break :blk bucket;
} else {
@panic("Invalid free");
}
}
}
self.freeLarge(old_mem, log2_old_align, ret_addr);
return;
};
const byte_offset = @intFromPtr(old_mem.ptr) - @intFromPtr(bucket.page);
const slot_index = @as(SlotIndex, @intCast(byte_offset / size_class));
const used_byte_index = slot_index / 8;
const used_bit_index = @as(u3, @intCast(slot_index % 8));
const used_byte = bucket.usedBits(used_byte_index);
const is_used = @as(u1, @truncate(used_byte.* >> used_bit_index)) != 0;
if (!is_used) {
if (config.safety) {
reportDoubleFree(ret_addr, bucketStackTrace(bucket, size_class, slot_index, .alloc), bucketStackTrace(bucket, size_class, slot_index, .free));
// Recoverable if this is a free.
return;
} else {
unreachable;
}
}
// Definitely an in-use small alloc now.
if (config.safety) {
const entry = self.small_allocations.getEntry(@intFromPtr(old_mem.ptr)) orelse
@panic("Invalid free");
if (old_mem.len != entry.value_ptr.requested_size or log2_old_align != entry.value_ptr.log2_ptr_align) {
var addresses: [stack_n]usize = [1]usize{0} ** stack_n;
var free_stack_trace = StackTrace{
.instruction_addresses = &addresses,
.index = 0,
};
std.debug.captureStackTrace(ret_addr, &free_stack_trace);
if (old_mem.len != entry.value_ptr.requested_size) {
log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {} Free: {}", .{
entry.value_ptr.requested_size,
old_mem.len,
bucketStackTrace(bucket, size_class, slot_index, .alloc),
free_stack_trace,
});
}
if (log2_old_align != entry.value_ptr.log2_ptr_align) {
log.err("Allocation alignment {d} does not match free alignment {d}. Allocation: {} Free: {}", .{
@as(usize, 1) << @as(math.Log2Int(usize), @intCast(entry.value_ptr.log2_ptr_align)),
@as(usize, 1) << @as(math.Log2Int(usize), @intCast(log2_old_align)),
bucketStackTrace(bucket, size_class, slot_index, .alloc),
free_stack_trace,
});
}
}
}
if (config.enable_memory_limit) {
self.total_requested_bytes -= old_mem.len;
}
// Capture stack trace to be the "first free", in case a double free happens.
bucket.captureStackTrace(ret_addr, size_class, slot_index, .free);
used_byte.* &= ~(@as(u8, 1) << used_bit_index);
bucket.used_count -= 1;
if (bucket.used_count == 0) {
if (bucket.next == bucket) {
// it's the only bucket and therefore the current one
self.buckets[bucket_index] = null;
} else {
bucket.next.prev = bucket.prev;
bucket.prev.next = bucket.next;
self.buckets[bucket_index] = bucket.prev;
}
if (!config.never_unmap) {
self.backing_allocator.free(bucket.page[0..page_size]);
}
if (!config.retain_metadata) {
self.freeBucket(bucket, size_class);
} else {
// move alloc_cursor to end so we can tell size_class later
const slot_count = @divExact(page_size, size_class);
bucket.alloc_cursor = @as(SlotIndex, @truncate(slot_count));
if (self.empty_buckets) |prev_bucket| {
// empty_buckets is ordered newest to oldest through prev so that if
// config.never_unmap is false and backing_allocator reuses freed memory
// then searchBuckets will always return the newer, relevant bucket
bucket.prev = prev_bucket;
bucket.next = prev_bucket.next;
prev_bucket.next = bucket;
bucket.next.prev = bucket;
} else {
bucket.prev = bucket;
bucket.next = bucket;
}
self.empty_buckets = bucket;
}
} else {
@memset(old_mem, undefined);
}
if (config.safety) {
assert(self.small_allocations.remove(@intFromPtr(old_mem.ptr)));
}
if (config.verbose_log) {
log.info("small free {d} bytes at {*}", .{ old_mem.len, old_mem.ptr });
}
}
// Returns true if an allocation of `size` bytes is within the specified
// limits if enable_memory_limit is true
fn isAllocationAllowed(self: *Self, size: usize) bool {
if (config.enable_memory_limit) {
const new_req_bytes = self.total_requested_bytes + size;
if (new_req_bytes > self.requested_memory_limit)
return false;
self.total_requested_bytes = new_req_bytes;
}
return true;
}
fn alloc(ctx: *anyopaque, len: usize, log2_ptr_align: u8, ret_addr: usize) ?[*]u8 {
const self: *Self = @ptrCast(@alignCast(ctx));
self.mutex.lock();
defer self.mutex.unlock();
if (!self.isAllocationAllowed(len)) return null;
return allocInner(self, len, @as(Allocator.Log2Align, @intCast(log2_ptr_align)), ret_addr) catch return null;
}
fn allocInner(
self: *Self,
len: usize,
log2_ptr_align: Allocator.Log2Align,
ret_addr: usize,
) Allocator.Error![*]u8 {
const new_aligned_size = @max(len, @as(usize, 1) << @as(Allocator.Log2Align, @intCast(log2_ptr_align)));
if (new_aligned_size > largest_bucket_object_size) {
try self.large_allocations.ensureUnusedCapacity(self.backing_allocator, 1);
const ptr = self.backing_allocator.rawAlloc(len, log2_ptr_align, ret_addr) orelse
return error.OutOfMemory;
const slice = ptr[0..len];
const gop = self.large_allocations.getOrPutAssumeCapacity(@intFromPtr(slice.ptr));
if (config.retain_metadata and !config.never_unmap) {
// Backing allocator may be reusing memory that we're retaining metadata for
assert(!gop.found_existing or gop.value_ptr.freed);
} else {
assert(!gop.found_existing); // This would mean the kernel double-mapped pages.
}
gop.value_ptr.bytes = slice;
if (config.enable_memory_limit)
gop.value_ptr.requested_size = len;
gop.value_ptr.captureStackTrace(ret_addr, .alloc);
if (config.retain_metadata) {
gop.value_ptr.freed = false;
if (config.never_unmap) {
gop.value_ptr.log2_ptr_align = log2_ptr_align;
}
}
if (config.verbose_log) {
log.info("large alloc {d} bytes at {*}", .{ slice.len, slice.ptr });
}
return slice.ptr;
}
if (config.safety) {
try self.small_allocations.ensureUnusedCapacity(self.backing_allocator, 1);
}
const new_size_class = math.ceilPowerOfTwoAssert(usize, new_aligned_size);
const ptr = try self.allocSlot(new_size_class, ret_addr);
if (config.safety) {
const gop = self.small_allocations.getOrPutAssumeCapacity(@intFromPtr(ptr));
gop.value_ptr.requested_size = len;
gop.value_ptr.log2_ptr_align = log2_ptr_align;
}
if (config.verbose_log) {
log.info("small alloc {d} bytes at {*}", .{ len, ptr });
}
return ptr;
}
fn createBucket(self: *Self, size_class: usize, bucket_index: usize) Error!*BucketHeader {
const page = try self.backing_allocator.alignedAlloc(u8, page_size, page_size);