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Refactor process_wait to add more comments and improve readability

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This commit is contained in:
sBubshait
2024-11-15 15:09:24 +00:00
parent 0f1bce2e88
commit a7f1d519da
1 changed files with 23 additions and 3 deletions
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26
src/userprog/process.c
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@@ -210,7 +210,8 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
so we can safely use strlen here. Filename has already been
split from the command line arguments. */
push_to_stack (esp, arg, strlen (arg) + 1);
/* Try to allocate memory for the argument pointer. */
struct arg_elem *arg_elem = malloc (sizeof (struct arg_elem));
if (arg_elem == NULL)
{
@@ -219,9 +220,11 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
return false;
}
/* Store the argument pointer in the linked list. */
arg_elem->arg = *esp;
list_push_front (&arg_list, &arg_elem->elem);
/* Increment the argument count and get the next argument. */
arg_count++;
arg = strtok_r (NULL, " ", &cmd_saveptr);
}
@@ -242,7 +245,10 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
int overflow_bytes = (PHYS_BASE - *esp) + remaining_size - PGSIZE;
if (overflow_bytes > 0)
{
/* Calculate the number of pages needed to allocate. */
int pages_needed = DIV_CEIL (overflow_bytes, PGSIZE);
/* Allocate the pages and map them to the user process. */
for (int i = 1; i < pages_needed + 1; i++)
{
uint8_t *kpage = palloc_get_page (PAL_USER | PAL_ZERO);
@@ -307,11 +313,12 @@ push_to_stack (void **esp, void *data, size_t data_size)
* This function will be implemented in task 2.
* For now, it does nothing. */
int
process_wait (tid_t child_tid UNUSED)
process_wait (tid_t child_tid)
{
struct process_result *child_result = NULL;
struct list_elem *e;
struct thread *cur = thread_current ();
for (e = list_begin (&cur->child_results);
e != list_end (&cur->child_results); e = list_next (e))
{
@@ -319,27 +326,40 @@ process_wait (tid_t child_tid UNUSED)
= list_entry (e, struct process_result, elem);
if (result->tid == child_tid)
{
/* Found the child process. */
child_result = result;
break;
}
/* List is ordered, allowing us to break early. */
/* List is ordered, allowing us to break early if the child_tid is
greater than the current result's tid. */
else if (result->tid > child_tid)
break;
}
/* If the child process was not found, return -1. */
if (child_result == NULL)
return -1;
/* Wait for child to die. */
sema_down (&child_result->sema);
/* We need lock release in process_exit, so we need to acquire (and possibly
wait) for it here to ensure we don't free the lock memory before it is
released in process_exit. */
lock_acquire (&child_result->lock);
/* To prevent waiting for child twice, remove it from the list.
No need to use lock since this is the only thread with access to
the struct process_result now. */
list_remove (&child_result->elem);
/* Get the exit status of the child */
int exit_status = child_result->exit_status;
/* Release the lock */
lock_release (&child_result->lock);
free (child_result);
return exit_status;
}