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/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Copyright (C) 2026 Richard Qin */
/*
* PID Allocator — Bitmap-based O(1) block search
* Reference: docs/specs/task.md §3.2
*/
#include <lume/pid.h>
void PidAllocator::init()
{
for (int i = 0; i < kBitmapWords; i++)
bitmap_[i] = 0;
next_hint_ = 1;
bitmap_[0] |= 0x1ULL; /* Reserve PID 0 (idle/swapper) only.
* PID 1 (init) is allocated normally — the first
* kthread_create() call gets it, matching Linux. */
}
int32 PidAllocator::alloc()
{
LockGuard guard(lock_);
int32 word_start = next_hint_ / 64;
for (int32 passes = 0; passes < kBitmapWords; passes++) {
int32 w = (word_start + passes) % kBitmapWords;
uint64 free_bits = ~bitmap_[w];
if (free_bits == 0)
continue;
int bit = 0;
uint64 v = free_bits;
while ((v & 1ULL) == 0) { v >>= 1; bit++; }
int32 pid = w * 64 + bit;
if (pid >= kMaxPid)
continue;
bitmap_[w] |= (1ULL << bit);
next_hint_ = pid + 1;
if (next_hint_ >= kMaxPid)
next_hint_ = 2;
return pid;
}
return -1;
}
void PidAllocator::free(int32 pid)
{
if (pid < 0 || pid >= kMaxPid)
return;
LockGuard guard(lock_);
int32 w = pid / 64;
int32 bit = pid % 64;
bitmap_[w] &= ~(1ULL << bit);
}
PidAllocator g_pid_alloc;
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