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Tristan/safer sighandler #75

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Tristan/safer sighandler #75

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6567b07
trying a safer approach
tjknoth Apr 20, 2024
a7d34c6
remove some code
tjknoth Apr 20, 2024
c37b811
data is no longer volatile
tjknoth Apr 20, 2024
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79 changes: 39 additions & 40 deletions runtime/process-posix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -28,12 +28,12 @@ typedef struct ChildProcess {
// NOTE: volatile declarations on 'next' forced by compiler.
typedef struct ChildProcessList {
ChildProcess* proc;
volatile struct ChildProcessList * volatile next;
volatile struct ChildProcessList * next;
} ChildProcessList;

// Linked list of live child processes.
// Will be read from by signal handler.
volatile ChildProcessList * volatile child_processes = NULL;
volatile ChildProcessList * child_processes = NULL;

// Add a new ChildProcess to the global 'child_processes' list.
// Precondition: SIGCHLD is blocked
Expand All @@ -47,39 +47,13 @@ void add_child_process (ChildProcess* child) {
// Return the ChildProcess with the given process id.
// Returns NULL if there is none.
static ChildProcess* get_child_process (pid_t pid){
volatile ChildProcessList * volatile curr = child_processes;
volatile ChildProcessList * curr = child_processes;
while(curr != NULL && curr->proc->pid != pid)
curr = curr->next;
if(curr == NULL) return NULL;
else return curr->proc;
}

// Remove the ChildProcess with the given process id from the
// 'child_processes' list if it exists in the list.
// Precondition: SIGCHLD is blocked
static void remove_child_process (pid_t pid) {

// Find the ChildProcess with matching pid.
// After this loop, either:
// 1. curr is NULL: No matching ChildProcess was found.
// 2. curr is ChildProcessList*: The matching ChildProcess was found.
volatile ChildProcessList * volatile curr = child_processes;
volatile ChildProcessList * volatile prev = NULL;
while(curr != NULL && curr->proc->pid != pid) {
prev = curr;
curr = curr->next;
}

// Remove child process from list if one was found.
if(curr != NULL){
if(prev == NULL)
child_processes = curr->next;
else
prev->next = curr->next;
free((void*) curr);
}
}

// After a child process is spawned, this function creates a
// ChildProcess struct for recording the child's metadata
// and stores it in the 'child_processes' list.
Expand Down Expand Up @@ -140,28 +114,46 @@ static void update_child_status (pid_t pid) {
int ret_pid = waitpid(pid, &status, WNOHANG | WUNTRACED | WCONTINUED);

//waitpid returns a positive integer if the process status has changed.
if(ret_pid > 0) {
if(ret_pid > 0)
set_child_status(pid, status);
// Remove the child's metadata from list if child is dead.
if(is_dead_status(status))
remove_child_process(pid);
}
}

// Update the current status of all registered child processes.
// Precondition: SIGCHLD is blocked
static void update_all_child_statuses () {
volatile ChildProcessList * volatile curr = child_processes;
volatile ChildProcessList * curr = child_processes;
while(curr != NULL) {
//NOTE: curr->next is retrieved preemptively because
//update_child_status may call free() on curr, and make
//curr->next inaccessible.
volatile ChildProcessList* next = curr->next;
update_child_status(curr->proc->pid);
curr = next;
curr = curr->next;
}
}

// Remove all ChildProcess nodes that have terminated from the list.
// Precondition: assumes SIGCHLD is blocked
static void remove_dead_child_processes () {
volatile ChildProcessList * curr = child_processes;
volatile ChildProcessList * prev = NULL;
while(curr != NULL) {
// Remove curr if its process has died
if(is_dead_status(*(curr->proc->status))) {
if(prev == NULL) {
child_processes = curr->next;
free((void*) curr);
curr = child_processes;
} else {
prev->next = curr->next;
free((void*) curr);
curr = prev->next;
}
} else {
prev = curr;
curr = curr->next;
}
}
}



//============================================================
//==================== Autoreap Handler ======================
//============================================================
Expand Down Expand Up @@ -326,6 +318,9 @@ stz_int launch_process(stz_byte* file, stz_byte** argvs,
//block sigchld
sigset_t old_signal_mask = block_sigchild();

//cleanup any unneeded process metadata
remove_dead_child_processes();

//Compute which pipes to create for the process.
//has_pipes[PROCESS_IN] = 1, indicates that a process input pipe
//needs to be created.
Expand Down Expand Up @@ -459,6 +454,7 @@ stz_int launch_process(stz_byte* file, stz_byte** argvs, stz_int input,
stz_int output, stz_int error,
stz_byte* working_dir, stz_byte** env_vars, Process* process) {


//Compute which pipes to create for the process.
//has_pipes[PROCESS_IN] = 1, indicates that a process input pipe
//needs to be created.
Expand Down Expand Up @@ -488,6 +484,9 @@ stz_int launch_process(stz_byte* file, stz_byte** argvs, stz_int input,
//Block SIGCHLD until setup is finished
sigset_t old_signal_mask = block_sigchild();

//cleanup any unneeded process metadata
remove_dead_child_processes();

//Set up the pipes in the parent process.
FILE* fin = NULL;
if(has_pipes[PROCESS_IN]) {
Expand Down