implement function to obtain active thread of a process

include/process.h

@@ -46,4 +46,10 @@ int determine_parent_process(process_status_t* list, size_t count, process_statu
 // get all process threads. for list and count same rules applies as for processes_by_name
 int process_get_threads(pid_t pid, process_status_t** list, size_t* count);
 
+// returns 1 if state considered active for a process/thread
+int is_considered_active(process_state_t state);
+
+// find any active (running) thread and returns 0 and success, otherwise non zero
+int find_active_thread(process_status_t* list, size_t count, process_status_t** thread);
+
 #endif

src/dummy_target.c

@@ -42,7 +42,9 @@ __attribute__((noreturn)) void* slave3_job(void*)
     puts("[slave3] will do something each second but in a thread");
     while (1)
     {
-        __asm__("nop");
+        unsigned a = 3;
+        for (unsigned i = 0; i < 100000; i++)
+            a = a * 3 - a;
         sleep(1);
     }
 }

src/main.c

@@ -1,3 +1,4 @@
+#define _DEFAULT_SOURCE
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -36,21 +37,39 @@ int main(int argc, char** argv)
 
     print_process(parent);
 
-    // get threads
+    // find active thread
+    puts("Looking for active thread..");
+    
     process_status_t* threads = NULL;
     size_t thread_count = 0;
-    if (process_get_threads(parent->pid, &threads, &thread_count))
+    
+    process_status_t* active;
+    while (1)
     {
-        fputs("failed to obtain process threads\n", stderr);
-        free(list);
-        return 1;
+        if (process_get_threads(parent->pid, &threads, &thread_count))
+        {
+            fputs("failed to obtain process threads\n", stderr);
+            free(list);
+            return 1;
+        }
+
+        if (find_active_thread(threads, thread_count, &active))
+        {
+            // no active threads - free list and continue
+            free(threads);
+            usleep(500*1000);
+        }
+        else
+        {
+            // we got active thread!
+            break;
+        }
     }
 
-    puts("Threads:");
-    for (size_t i = 0; i < thread_count; i++)
-        print_process(&threads[i]);
+    puts("Active thread:");
+    print_process(active);
 
-    free(list);
     free(threads);
+    free(list);
     return 0;
 }

src/process.c

@@ -67,6 +67,9 @@ static int is_numeric(const char* str)
 
 int processes_by_name(const char* name, process_status_t** list, size_t* count)
 {
+    *list = NULL;
+    *count = 0;
+
     DIR* proc = opendir("/proc");
     if (!proc) return 1;
 
@@ -140,6 +143,9 @@ int determine_parent_process(process_status_t* list, size_t count, process_statu
 
 int process_get_threads(pid_t pid, process_status_t** list, size_t* count)
 {
+    *list = NULL;
+    *count = 0;
+
     char taskPath[256] = {0};
     snprintf(taskPath, sizeof(taskPath), "/proc/%d/task", pid);
 
@@ -187,3 +193,22 @@ int process_get_threads(pid_t pid, process_status_t** list, size_t* count)
     closedir(taskDir);
     return 0;
 }
+
+int is_considered_active(process_state_t state)
+{
+    return state == INTERRUPTIBLE_SLEEP || state == RUNNING;
+}
+
+int find_active_thread(process_status_t* list, size_t count, process_status_t** thread)
+{
+    for (size_t i = 0; i < count; i++)
+    {
+        TRACE("task %d state %d\n", list[i].pid, list[i].state);
+        if (is_considered_active(list[i].state))
+        {
+            *thread = &list[i];
+            return 0;
+        }
+    }
+    return 1;
+}