How to Monitor Multi‑Threaded Linux Processes with top -H

This example demonstrates how to create multiple POSIX threads, assign each a distinct name, and observe them with standard Linux monitoring tools.

Source file: multi_thread.c

#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// Maximum thread name length
#define APP_THREAD_NAME_MAX_LEN 32

typedef enum {
    APP_THREAD_INDEX_TEST0,
    APP_THREAD_INDEX_TEST1,
    APP_THREAD_INDEX_TEST2,
    APP_THREAD_INDEX_TEST3,
    APP_THREAD_INDEX_TEST4,
    APP_THREAD_INDEX_TEST5,
    APP_THREAD_INDEX_MAX
} app_thread_index_e;

typedef void *(*p_thread_fun)(void *param);

typedef struct {
    pthread_t thread_handle;
    p_thread_fun thread_entry;
    char name[APP_THREAD_NAME_MAX_LEN];
} app_thread_s;

static void *test0_thread_entry(void *param);
static void *test1_thread_entry(void *param);
static void *test2_thread_entry(void *param);
static void *test3_thread_entry(void *param);
static void *test4_thread_entry(void *param);
static void *test5_thread_entry(void *param);

app_thread_s s_app_thread_table[APP_THREAD_INDEX_MAX] = {
    {0, test0_thread_entry, "test0_thread"},
    {0, test1_thread_entry, "test1_thread"},
    {0, test2_thread_entry, "test2_thread"},
    {0, test3_thread_entry, "test3_thread"},
    {0, test4_thread_entry, "test4_thread"},
    {0, test5_thread_entry, "test5_thread"}
};

static void *test0_thread_entry(void *param) {
    printf("test0_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}
static void *test1_thread_entry(void *param) {
    printf("test1_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}
static void *test2_thread_entry(void *param) {
    printf("test2_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}
static void *test3_thread_entry(void *param) {
    printf("test3_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}
static void *test4_thread_entry(void *param) {
    printf("test4_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}
static void *test5_thread_entry(void *param) {
    printf("test5_thread running...
");
    while (1) { usleep(2 * 1000); }
    return NULL;
}

static int create_all_app_thread(void) {
    int ret = 0;
    for (int i = 0; i < APP_THREAD_INDEX_MAX; i++) {
        ret = pthread_create(&s_app_thread_table[i].thread_handle, NULL,
                             s_app_thread_table[i].thread_entry, NULL);
        if (ret != 0) {
            printf("%s thread create error! thread_id = %ld
",
                   s_app_thread_table[i].name, s_app_thread_table[i].thread_handle);
            return ret;
        }
        printf("%s thread create success! thread_id = %ld
",
               s_app_thread_table[i].name, s_app_thread_table[i].thread_handle);
        pthread_setname_np(s_app_thread_table[i].thread_handle,
                           s_app_thread_table[i].name);
        pthread_detach(s_app_thread_table[i].thread_handle);
    }
    return ret;
}

int main(int argc, char **argv) {
    create_all_app_thread();
    while (1) { usleep(2 * 1000); }
    return 0;
}

Compile the program with a POSIX‑thread aware compiler, for example: gcc -pthread multi_thread.c -o multi_thread Run the executable, then use the top utility to list each thread separately: top -H -p `pidof multi_thread` The -H flag tells top to display threads instead of just processes. The back‑ticks around pidof multi_thread are required to substitute the process ID at runtime.

Because each thread is named with pthread_setname_np, top shows the custom names (e.g., test0_thread , test1_thread , …). If the naming call is omitted, top will display the parent process name for every thread, making it impossible to distinguish them.

Thus, assigning names to threads via pthread_setname_np is essential for effective per‑thread monitoring on Linux.