Arena initial implementation.

Signed-off-by: Mitja Horvat <mitja@plume.com>

src/scratch.c

@@ -0,0 +1,81 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "scratch.h"
+
+#if __STDC_VERSION__ >= 201112L /* C11 and above */
+#define thread_local _Thread_local
+#elif defined(__GNUC__)
+#define thread_local __thread
+#else
+#error Unsupported compiler.
+#endif
+
+#if defined(__GNUC__)
+#define WEAK __attribute__((weak))
+#endif
+
+thread_local arena_t *scratch_arena[4] = { 0 };
+
+void scratch_destroy(void)
+{
+    for (int s = 0; s < sizeof(scratch_arena) / sizeof(scratch_arena[0]); s++)
+    {
+        if (scratch_arena[s] == NULL) continue;
+        arena_del(scratch_arena[s]);
+        scratch_arena[s] = NULL;
+    }
+}
+
+/*
+ * Optionally allocate and return a scratch arena. Make sure that the returned
+ * arena is not present in the NULL-terminated list `conflicts`
+ */
+arena_t *__scratch_get(arena_t **conflicts)
+{
+    int s = 0;
+
+    if (conflicts != NULL)
+    {
+        for (s = 0; s < sizeof(scratch_arena) / sizeof(scratch_arena[0]); s++)
+        {
+            arena_t **c = conflicts;
+            for (; *c != NULL; c++)
+            {
+                if (*c == scratch_arena[s]) break;
+            }
+            /* No conflcits found, break out */
+            if (*c == NULL) break;
+        }
+        if (s >= sizeof(scratch_arena) / sizeof(scratch_arena[0]))
+        {
+            fprintf(stderr, "Out of scratch arenas.\n");
+            return NULL;
+        }
+    }
+
+    if (scratch_arena[s] == NULL)
+    {
+        scratch_cleanup_init();
+        scratch_arena[s] = arena_new(SCRATCH_DEFAULT_SIZE);
+        if (scratch_arena[s] == NULL)
+        {
+            fprintf(stderr, "Error allocating scratch arena %d.", s);
+            return NULL;
+        }
+
+        printf("NEW SCRATCH = %p\n", scratch_arena[s]);
+    }
+
+    return scratch_arena[s];
+}
+
+void WEAK scratch_cleanup_init(void)
+{
+    static bool init = false;
+    for (;!init; init = true)
+    {
+        printf("Single-threaded mode.\n");
+        atexit(scratch_destroy);
+    }
+}