Function __pthread_create

system/lib/pthread/pthread_create.c:107–270

#define ROUND_UP(x, ALIGNMENT) (((x)+ALIGNMENT-1)&-ALIGNMENT)

int __pthread_create(pthread_t* restrict res,
                     const pthread_attr_t* restrict attrp,
                     void* (*entry)(void*),
                     void* restrict arg) {
  // Note on LSAN: lsan intercepts/wraps calls to pthread_create so any
  // allocations we do here should not be considered leaks.
  // See: lsan_interceptors.cpp.
  if (!res) {
    return EINVAL;
  }

  if (!libc.threaded) {
    for (FILE *f=*__ofl_lock(); f; f=f->next)
      init_file_lock(f);
    __ofl_unlock();
    init_file_lock(__stdin_used);
    init_file_lock(__stdout_used);
    init_file_lock(__stderr_used);
    libc.threaded = 1;
  }

  pthread_attr_t attr = { 0 };
  if (attrp && attrp != __ATTRP_C11_THREAD) attr = *attrp;
  if (!attr._a_stacksize) {
    attr._a_stacksize = __default_stacksize;
  }

  // Allocate memory for new thread.  The layout of the thread block is
  // as follows.  From low to high address:
  //
  // 1. pthread struct (sizeof struct pthread)
  // 2. tls data       (__builtin_wasm_tls_size())
  // 3. tsd pointers   (__pthread_tsd_size)
  // 4. stack          (__default_stacksize AKA -sDEFAULT_PTHREAD_STACK_SIZE)
  size_t size = sizeof(struct pthread);
  if (__builtin_wasm_tls_size()) {
    size += __builtin_wasm_tls_size() + __builtin_wasm_tls_align() - 1;
  }
  size += __pthread_tsd_size + TSD_ALIGN - 1;
  size_t zero_size = size;
  if (!attr._a_stackaddr) {
    size += attr._a_stacksize + STACK_ALIGN - 1;
  }

  // Allocate all the data for the new thread and zero-initialize all parts
  // except for the stack.
  unsigned char* block = emscripten_builtin_malloc(size);
  memset(block, 0, zero_size);

  uintptr_t offset = (uintptr_t)block;

  // 1. pthread struct
  struct pthread *new = (struct pthread*)offset;
  offset += sizeof(struct pthread);

  new->map_base = block;
  new->map_size = size;