hashers now use thread local arena

Instead of writing directly to file_hashes.txt, hash_workers now are
using a local arena, writing everything once at the end

using #pragma once to ensure that a given header file is included only
once in a single compilation unit

platform_windows.c

@@ -1,5 +1,4 @@
 #include "platform.h"
-#include <stdio.h>
 
 // ----------------------------- Globals ------------------------------------
 static atomic_uint_fast64_t g_files_found = 0;
@@ -409,14 +408,10 @@ static void xxh3_hash_file_stream(const char *path, char *out_hex) {
 
 // ------------------------- Hash worker --------------------------------
 static DWORD WINAPI hash_worker(LPVOID arg) {
-  MPMCQueue *q = (MPMCQueue *)arg;
 
-  static CRITICAL_SECTION append_cs;
-  static LONG init = 0;
-
-  if (InterlockedCompareExchange(&init, 1, 0) == 0) {
-    InitializeCriticalSection(&append_cs);
-  }
+  WorkerContext *ctx = (WorkerContext *)arg;
+  MPMCQueue *q = ctx->queue;
+  mem_arena *local_arena = ctx->arena;
 
   for (;;) {
     FileEntry *fe = mpmc_pop(q);
@@ -432,16 +427,14 @@ static DWORD WINAPI hash_worker(LPVOID arg) {
 
     double size_kib = (double)fe->size_bytes / 1024.0;
 
-    EnterCriticalSection(&append_cs);
+    char stack_buf[1024];
 
-    FILE *hf = fopen(FILE_HASHES_TXT, "a");
-    if (hf) {
-      fprintf(hf, "%s\t%s\t%.2f\t%s\t%s\t%s\n", hash, fe->path, size_kib,
-              created, modified, fe->owner);
-      fclose(hf);
-    }
+    int len =
+        snprintf(stack_buf, sizeof(stack_buf), "%s\t%s\t%.2f\t%s\t%s\t%s\n",
+                 hash, fe->path, size_kib, created, modified, fe->owner);
 
-    LeaveCriticalSection(&append_cs);
+    char *dst = arena_push(&local_arena, len, false);
+    memcpy(dst, stack_buf, len);
 
     atomic_fetch_add(&g_files_hashed, 1);
 
@@ -627,7 +620,7 @@ int main(int argc, char **argv) {
   // Step 1: Scan all folders
   // -------------------------------
 
-  mpmc_init(&g_file_queue, 1024 * 1024 * 1024);
+  mpmc_init(&g_file_queue, GiB(1));
 
   DirQueue q;
   memset(&q, 0, sizeof(q));
@@ -636,11 +629,30 @@ int main(int argc, char **argv) {
   q.active = 0;
 
   // starting hash threads
+
+  arena_params params = {
+      .reserve_size = GiB(1),
+      .commit_size = MiB(16),
+      .align = 0,
+      .push_size = 0,
+      .allow_free_list = true,
+      .allow_swapback = false,
+      .growth_policy = ARENA_GROWTH_NORMAL,
+      .commit_policy = ARENA_COMMIT_LAZY,
+      .max_nbre_blocks = 0,
+  };
+
+  WorkerContext workers[num_threads];
+
+  for (int i = 0; i < num_threads; i++) {
+    workers[i].queue = &g_file_queue;
+    workers[i].arena = arena_create(&params);
+  }
+
   HANDLE *hash_threads = malloc(sizeof(HANDLE) * num_threads);
 
   for (size_t i = 0; i < num_threads; ++i) {
-    hash_threads[i] =
-        CreateThread(NULL, 0, hash_worker, &g_file_queue, 0, NULL);
+    hash_threads[i] = CreateThread(NULL, 0, hash_worker, &workers[i], 0, NULL);
   }
 
   // starting scan threads
@@ -662,7 +674,6 @@ int main(int argc, char **argv) {
 
   WaitForMultipleObjects((DWORD)scan_threads, scan_tids, TRUE, INFINITE);
 
-  // mpmc_finish(&g_file_queue);
   // debug
   for (size_t i = 0; i < num_threads; i++) {
     mpmc_push(&g_file_queue, NULL);
@@ -694,11 +705,39 @@ int main(int argc, char **argv) {
     CloseHandle(hash_threads[i]);
 
   free(hash_threads);
-  // free(g_file_queue.items);
 
   WaitForSingleObject(progress, INFINITE);
   CloseHandle(progress);
 
+  // write file_hashes.txt
+
+  // FILE *f = fopen(FILE_HASHES_TXT, "wb");
+  //
+  // for (int i = 0; i < num_threads; i++) {
+  //   mem_arena *arena = workers[i].arena;
+  //
+  //   u8 *arena_base =
+  //       (u8 *)arena + ALIGN_UP_POW2(sizeof(mem_arena), arena->align);
+  //   fwrite(arena_base, 1, arena->pos, f);
+  // }
+  //
+  // fclose(f);
+
+  HANDLE h = CreateFileA(FILE_HASHES_TXT, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
+                         FILE_ATTRIBUTE_NORMAL, NULL);
+
+  for (int i = 0; i < num_threads; i++) {
+
+    mem_arena *arena = workers[i].arena;
+
+    DWORD written;
+
+    u8 *arena_base =
+        (u8 *)arena + ALIGN_UP_POW2(sizeof(mem_arena), arena->align);
+
+    WriteFile(h, arena_base, (DWORD)arena->pos, &written, NULL);
+  }
+
   // done time
   double total_seconds = timer_stop(&total_timer);