wait-free global region allocator...

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#define REGION_SIZE (4096 * 1024)

struct region {
  unsigned char buf[REGION_SIZE];
  atomicuword volatile offset; /* == 0 */
};

static void* 
galloc(
 struct region* const this,
 size_t const size
) {
  atomicuword offset;
  if (this->offset + size >= REGION_SIZE) {
    return NULL;
  }
  offset = XADD(&this->offset, size);
  if (offset + size >= REGION_SIZE) {
    return NULL;
  }
  return this->buf + offset;
}

static void 
gflush(
 struct region* const this
) {
  XCHG(&this->offset, 0);
}
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Simple.