// Copyright 2023 Google LLC
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Modified from BSD-licensed code
// Copyright (c) the JPEG XL Project Authors. All rights reserved.
// See https://github.com/libjxl/libjxl/blob/main/LICENSE.

#include "hwy/contrib/thread_pool/thread_pool.h"

#include <math.h>  // sqrtf
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

#include <atomic>
#include <vector>

#include "gtest/gtest.h"
#include "hwy/base.h"                  // PopCount
#include "hwy/detect_compiler_arch.h"  // HWY_ARCH_WASM
#include "hwy/tests/test_util-inl.h"   // AdjustedReps

namespace hwy {
namespace {
using HWY_NAMESPACE::AdjustedReps;

// Exhaustive test for small/large dividends and divisors
TEST(ThreadPoolTest, TestDivisor) {
  // Small d, small n
  for (uint32_t d = 1; d < 256; ++d) {
    const Divisor divisor(d);
    for (uint32_t n = 0; n < 256; ++n) {
      HWY_ASSERT(divisor.Divide(n) == n / d);
      HWY_ASSERT(divisor.Remainder(n) == n % d);
    }
  }

  // Large d, small n
  for (uint32_t d = 0xFFFFFF00u; d != 0; ++d) {
    const Divisor divisor(d);
    for (uint32_t n = 0; n < 256; ++n) {
      HWY_ASSERT(divisor.Divide(n) == n / d);
      HWY_ASSERT(divisor.Remainder(n) == n % d);
    }
  }

  // Small d, large n
  for (uint32_t d = 1; d < 256; ++d) {
    const Divisor divisor(d);
    for (uint32_t n = 0xFFFFFF00u; n != 0; ++n) {
      HWY_ASSERT(divisor.Divide(n) == n / d);
      HWY_ASSERT(divisor.Remainder(n) == n % d);
    }
  }

  // Large d, large n
  for (uint32_t d = 0xFFFFFF00u; d != 0; ++d) {
    const Divisor divisor(d);
    for (uint32_t n = 0xFFFFFF00u; n != 0; ++n) {
      HWY_ASSERT(divisor.Divide(n) == n / d);
      HWY_ASSERT(divisor.Remainder(n) == n % d);
    }
  }
}

TEST(ThreadPoolTest, TestCoprime) {
  // 1 is coprime with anything
  for (uint32_t i = 1; i < 500; ++i) {
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(1, i));
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(i, 1));
  }

  // Powers of two >= 2 are not coprime
  for (size_t i = 1; i < 20; ++i) {
    for (size_t j = 1; j < 20; ++j) {
      HWY_ASSERT(!ShuffledIota::CoprimeNonzero(1u << i, 1u << j));
    }
  }

  // 2^x and 2^x +/- 1 are coprime
  for (size_t i = 1; i < 30; ++i) {
    const uint32_t pow2 = 1u << i;
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(pow2, pow2 + 1));
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(pow2, pow2 - 1));
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(pow2 + 1, pow2));
    HWY_ASSERT(ShuffledIota::CoprimeNonzero(pow2 - 1, pow2));
  }

  // Random number x * random y (both >= 2) is not co-prime with x nor y.
  RandomState rng;
  for (size_t i = 1; i < 5000; ++i) {
    const uint32_t x = (Random32(&rng) & 0xFFF7) + 2;
    const uint32_t y = (Random32(&rng) & 0xFFF7) + 2;
    HWY_ASSERT(!ShuffledIota::CoprimeNonzero(x * y, x));
    HWY_ASSERT(!ShuffledIota::CoprimeNonzero(x * y, y));
    HWY_ASSERT(!ShuffledIota::CoprimeNonzero(x, x * y));
    HWY_ASSERT(!ShuffledIota::CoprimeNonzero(y, x * y));
  }

  // Primes are all coprime (list from https://oeis.org/A000040)
  static constexpr uint32_t primes[] = {
      2,   3,   5,   7,   11,  13,  17,  19,  23,  29,  31,  37,  41,  43,  47,
      53,  59,  61,  67,  71,  73,  79,  83,  89,  97,  101, 103, 107, 109, 113,
      127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197,
      199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271};
  for (size_t i = 0; i < sizeof(primes) / sizeof(primes[0]); ++i) {
    for (size_t j = i + 1; j < sizeof(primes) / sizeof(primes[0]); ++j) {
      HWY_ASSERT(ShuffledIota::CoprimeNonzero(primes[i], primes[j]));
      HWY_ASSERT(ShuffledIota::CoprimeNonzero(primes[j], primes[i]));
    }
  }
}

// Ensures `shuffled` visits [0, size) exactly once starting from `current`.
void VerifyPermutation(uint32_t size, const Divisor& divisor,
                       const ShuffledIota& shuffled, uint32_t current,
                       uint32_t* visited) {
  for (size_t i = 0; i < size; i++) {
    visited[i] = 0;
  }

  for (size_t i = 0; i < size; i++) {
    ++visited[current];
    current = shuffled.Next(current, divisor);
  }

  for (size_t i = 0; i < size; i++) {
    HWY_ASSERT(visited[i] == 1);
  }
}

// Verifies ShuffledIota generates a permutation of [0, size).
TEST(ThreadPoolTest, TestRandomPermutation) {
  constexpr size_t kMaxSize = 40;
  uint32_t visited[kMaxSize];

  // Exhaustive enumeration of size and starting point.
  for (uint32_t size = 1; size < kMaxSize; ++size) {
    const Divisor divisor(size);

    const uint32_t coprime = ShuffledIota::FindAnotherCoprime(size, 1);
    const ShuffledIota shuffled(coprime);

    for (uint32_t start = 0; start < size; ++start) {
      VerifyPermutation(size, divisor, shuffled, start, visited);
    }
  }
}

// Verifies multiple ShuffledIota are relatively independent.
TEST(ThreadPoolTest, TestMultiplePermutations) {
  constexpr size_t kMaxSize = 40;
  uint32_t coprimes[kMaxSize];
  // One per ShuffledIota; initially the starting value, then its Next().
  uint32_t current[kMaxSize];

  for (uint32_t size = 1; size < kMaxSize; ++size) {
    const Divisor divisor(size);

    // Create `size` ShuffledIota instances with unique coprimes.
    std::vector<ShuffledIota> shuffled;
    for (size_t i = 0; i < size; ++i) {
      coprimes[i] = ShuffledIota::FindAnotherCoprime(
          size, static_cast<uint32_t>((i + 1) * 257 + i * 13));
      shuffled.emplace_back(coprimes[i]);
    }

    // ShuffledIota[i] starts at i to match the worker thread use case.
    for (uint32_t i = 0; i < size; ++i) {
      current[i] = i;
    }

    size_t num_bad = 0;
    uint32_t all_visited[kMaxSize] = {0};

    // For each step, ensure there are few non-unique current[].
    for (size_t step = 0; step < size; ++step) {
      // How many times is each number visited?
      uint32_t visited[kMaxSize] = {0};
      for (size_t i = 0; i < size; ++i) {
        visited[current[i]] += 1;
        all_visited[current[i]] = 1;  // visited at all across all steps?
      }

      // How many numbers are visited multiple times?
      size_t num_contended = 0;
      uint32_t max_contention = 0;
      for (size_t i = 0; i < size; ++i) {
        num_contended += visited[i] > 1;
        max_contention = HWY_MAX(max_contention, visited[i]);
      }

      // Count/print if excessive collisions.
      const size_t expected =
          static_cast<size_t>(sqrtf(static_cast<float>(size)) * 2.0f);
      if ((num_contended > expected) && (max_contention > 3)) {
        ++num_bad;
        if (true) {
          fprintf(stderr, "size %u step %zu contended %zu max contention %u\n",
                  size, step, num_contended, max_contention);
          for (size_t i = 0; i < size; ++i) {
            fprintf(stderr, "  %u\n", current[i]);
          }
          fprintf(stderr, "coprimes\n");
          for (size_t i = 0; i < size; ++i) {
            fprintf(stderr, "  %u\n", coprimes[i]);
          }
        }
      }

      // Advance all ShuffledIota generators.
      for (size_t i = 0; i < size; ++i) {
        current[i] = shuffled[i].Next(current[i], divisor);
      }
    }  // step

    // Ensure each task was visited during at least one step.
    for (size_t i = 0; i < size; ++i) {
      HWY_ASSERT(all_visited[i] != 0);
    }

    if (num_bad != 0) {
      fprintf(stderr, "size %u total bad: %zu\n", size, num_bad);
    }
    HWY_ASSERT(num_bad < kMaxSize / 10);
  }  // size
}

// Ensures all tasks are run. Similar to TestPool below but without threads.
TEST(ThreadPoolTest, TestTasks) {
  for (size_t num_threads = 0; num_threads <= 8; ++num_threads) {
    PoolMemOwner owner(num_threads);
    PoolMem& mem = *owner.Mem();
    const size_t num_workers = owner.NumWorkers();

    constexpr uint64_t kMaxTasks = 20;
    uint64_t mementos[kMaxTasks];
    for (uint64_t num_tasks = 0; num_tasks < 20; ++num_tasks) {
      for (uint64_t begin = 0; begin < AdjustedReps(32); ++begin) {
        const uint64_t end = begin + num_tasks;

        ZeroBytes(mementos, sizeof(mementos));
        const auto func = [begin, end, &mementos](uint64_t task,
                                                  size_t /*thread*/) {
          HWY_ASSERT(begin <= task && task < end);

          // Store mementos ensure we visited each task.
          mementos[task - begin] = 1000 + task;
        };

        if (ParallelFor::Plan(begin, end, num_workers, func, mem)) {
          // The `tasks < workers` special case requires running by all workers.
          for (size_t thread = 0; thread < num_workers; ++thread) {
            ParallelFor::WorkerRun(thread, num_workers, mem);
          }
        }

        // Ensure all tasks were run.
        for (uint64_t task = begin; task < end; ++task) {
          HWY_ASSERT_EQ(1000 + task, mementos[task - begin]);
        }
      }
    }
  }
}

// Ensures old code with 32-bit tasks and InitClosure still compiles.
TEST(ThreadPoolTest, TestDeprecated) {
  ThreadPool pool(0);
  pool.Run(1, 10, &ThreadPool::NoInit,
           [&](const uint64_t /*task*/, size_t /*thread*/) {});
}

// Ensures task parameter is in bounds, every parameter is reached,
// pool can be reused (multiple consecutive Run calls), pool can be destroyed
// (joining with its threads), num_threads=0 works (runs on current thread).
TEST(ThreadPoolTest, TestPool) {
  if (HWY_ARCH_WASM) return;  // WASM threading is unreliable

  ThreadPool inner(0);

  for (size_t num_threads = 0; num_threads <= 6; num_threads += 3) {
    ThreadPool pool(HWY_MIN(ThreadPool::MaxThreads(), num_threads));

    constexpr uint64_t kMaxTasks = 20;
    std::atomic<uint64_t> mementos[kMaxTasks];
    for (uint64_t num_tasks = 0; num_tasks < kMaxTasks; ++num_tasks) {
      for (uint64_t begin = 0; begin < AdjustedReps(32); ++begin) {
        const uint64_t end = begin + num_tasks;
        std::atomic<uint64_t> a_begin;
        std::atomic<uint64_t> a_end;
        a_begin.store(begin, std::memory_order_release);
        a_end.store(end, std::memory_order_release);

        for (size_t i = 0; i < kMaxTasks; ++i) {
          mementos[i].store(0);
        }
        pool.Run(begin, end,
                 [&a_begin, &a_end, &mementos, &inner](uint64_t task,
                                                       size_t /*thread*/) {
                   const uint64_t begin =
                       a_begin.load(std::memory_order_acquire);
                   const uint64_t end = a_end.load(std::memory_order_acquire);
                   HWY_ASSERT(begin <= task && task < end);

                   // Store mementos ensure we visited each task.
                   mementos[task - begin].store(1000 + task);

                   // Re-entering Run is fine on a 0-worker pool.
                   inner.Run(begin, end,
                             [begin, end](uint64_t task, size_t /*thread*/) {
                               HWY_ASSERT(begin <= task && task < end);
                             });
                 });

        for (uint64_t task = begin; task < end; ++task) {
          HWY_ASSERT_EQ(1000 + task, mementos[task - begin].load());
        }
      }
    }
  }
}

// Debug tsan builds seem to generate incorrect codegen for [&] of atomics, so
// use a pointer to a state object instead.
struct SmallAssignmentState {
  // (Avoid mutex because it may perturb the worker thread scheduling)
  std::atomic<uint64_t> num_tasks{0};
  std::atomic<uint64_t> num_workers{0};
  std::atomic<uint64_t> id_bits{0};
  std::atomic<uint64_t> num_calls{0};
};

// Verify "thread" parameter when processing few tasks.
TEST(ThreadPoolTest, TestSmallAssignments) {
  if (HWY_ARCH_WASM) return;  // WASM threading is unreliable

  static SmallAssignmentState state;

  for (size_t num_threads :
       {size_t{0}, size_t{1}, size_t{3}, size_t{5}, size_t{8}}) {
    ThreadPool pool(HWY_MIN(ThreadPool::MaxThreads(), num_threads));
    state.num_workers.store(pool.NumWorkers());

    for (size_t mul = 1; mul <= 2; ++mul) {
      const size_t num_tasks = pool.NumWorkers() * mul;
      state.num_tasks.store(num_tasks);
      state.id_bits.store(0);
      state.num_calls.store(0);

      pool.Run(0, num_tasks, [](uint64_t task, size_t thread) {
        HWY_ASSERT(task < state.num_tasks.load());
        HWY_ASSERT(thread < state.num_workers.load());

        state.num_calls.fetch_add(1);

        uint64_t bits = state.id_bits.load();
        while (!state.id_bits.compare_exchange_weak(bits,
                                                    bits | (1ULL << thread))) {
        }
      });

      // Correct number of tasks.
      const uint64_t actual_calls = state.num_calls.load();
      HWY_ASSERT(num_tasks == actual_calls);

      const size_t num_participants = PopCount(state.id_bits.load());
      // <= because some workers may not manage to run any tasks.
      HWY_ASSERT(num_participants <= pool.NumWorkers());
    }
  }
}

struct Counter {
  Counter() {
    // Suppress "unused-field" warning.
    (void)padding;
  }
  void Assimilate(const Counter& victim) { counter += victim.counter; }
  std::atomic<uint64_t> counter{0};
  uint64_t padding[15];
};

// Can switch between any wait mode, and multiple times.
TEST(ThreadPoolTest, TestWaitMode) {
  if (HWY_ARCH_WASM) return;  // WASM threading is unreliable

  const size_t kNumThreads = 9;
  ThreadPool pool(kNumThreads);
  RandomState rng;
  for (size_t i = 0; i < 10; ++i) {
    pool.SetWaitMode(Random32(&rng) ? PoolWaitMode::kSpin
                                    : PoolWaitMode::kBlock);
  }
}

TEST(ThreadPoolTest, TestCounter) {
  if (HWY_ARCH_WASM) return;  // WASM threading is unreliable

  const size_t kNumThreads = 12;
  ThreadPool pool(kNumThreads);
  for (PoolWaitMode mode : {PoolWaitMode::kSpin, PoolWaitMode::kBlock}) {
    pool.SetWaitMode(mode);
    alignas(128) Counter counters[kNumThreads];

    const uint64_t kNumTasks = kNumThreads * 19;
    pool.Run(0, kNumTasks,
             [&counters](const uint64_t task, const size_t thread) {
               counters[thread].counter.fetch_add(task);
             });

    uint64_t expected = 0;
    for (uint64_t i = 0; i < kNumTasks; ++i) {
      expected += i;
    }

    for (size_t i = 1; i < kNumThreads; ++i) {
      counters[0].Assimilate(counters[i]);
    }
    HWY_ASSERT_EQ(expected, counters[0].counter.load());
  }
}

}  // namespace
}  // namespace hwy