diff --git a/.vscode/tasks.json b/.vscode/tasks.json
new file mode 100644
index 0000000..5d4653d
--- /dev/null
+++ b/.vscode/tasks.json
@@ -0,0 +1,28 @@
+{
+    "tasks": [
+        {
+            "type": "cppbuild",
+            "label": "C/C++: gcc 生成活动文件",
+            "command": "/usr/bin/gcc",
+            "args": [
+                "-fdiagnostics-color=always",
+                "-g",
+                "${file}",
+                "-o",
+                "${fileDirname}/${fileBasenameNoExtension}"
+            ],
+            "options": {
+                "cwd": "${fileDirname}"
+            },
+            "problemMatcher": [
+                "$gcc"
+            ],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "detail": "调试器生成的任务。"
+        }
+    ],
+    "version": "2.0.0"
+}
\ No newline at end of file
diff --git a/exp1/.vscode/launch.json b/exp1/.vscode/launch.json
new file mode 100644
index 0000000..f980ab9
--- /dev/null
+++ b/exp1/.vscode/launch.json
@@ -0,0 +1,7 @@
+{
+    // 使用 IntelliSense 了解相关属性。 
+    // 悬停以查看现有属性的描述。
+    // 欲了解更多信息，请访问: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": []
+}
\ No newline at end of file
diff --git a/exp1/.vscode/tasks.json b/exp1/.vscode/tasks.json
new file mode 100644
index 0000000..5d4653d
--- /dev/null
+++ b/exp1/.vscode/tasks.json
@@ -0,0 +1,28 @@
+{
+    "tasks": [
+        {
+            "type": "cppbuild",
+            "label": "C/C++: gcc 生成活动文件",
+            "command": "/usr/bin/gcc",
+            "args": [
+                "-fdiagnostics-color=always",
+                "-g",
+                "${file}",
+                "-o",
+                "${fileDirname}/${fileBasenameNoExtension}"
+            ],
+            "options": {
+                "cwd": "${fileDirname}"
+            },
+            "problemMatcher": [
+                "$gcc"
+            ],
+            "group": {
+                "kind": "build",
+                "isDefault": true
+            },
+            "detail": "调试器生成的任务。"
+        }
+    ],
+    "version": "2.0.0"
+}
\ No newline at end of file
diff --git a/exp1/badcount b/exp1/badcount
new file mode 100755
index 0000000..01e7892
Binary files /dev/null and b/exp1/badcount differ
diff --git a/exp1/badcount.c b/exp1/badcount.c
new file mode 100644
index 0000000..3b6acf9
--- /dev/null
+++ b/exp1/badcount.c
@@ -0,0 +1,62 @@
+#include <pthread.h>
+#include <time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int cnt = 0;
+sem_t mutex;
+
+void *increase(void *vargp)
+{
+    unsigned int niters = (unsigned int)vargp;
+    for (unsigned int i = 0; i < niters; i++)
+    {
+        sem_wait(&mutex);
+        cnt++;
+        sem_post(&mutex);
+    }
+    return NULL;
+}
+
+void *decrease(void *vargp)
+{
+    unsigned int niters = (unsigned int)vargp;
+    for (unsigned int i = 0; i < niters; i++)
+    {
+        sem_wait(&mutex);
+        cnt--;
+        sem_post(&mutex);
+    }
+    return NULL;
+}
+
+int main(int argc, char **argv)
+{
+    unsigned int niters;
+    pthread_t t1,t2;
+
+    if (argc != 2)
+    {
+        printf("Usage: %s <niters>\n", argv[0]);
+        exit(2);
+    }
+    niters = atoll(argv[1]);
+
+    sem_init(&mutex, 0, 1);
+    pthread_create(&t1,NULL,increase,(void*)niters);
+    pthread_create(&t2,NULL,decrease,(void*)niters);
+    pthread_join(t1,NULL);
+    pthread_join(t2,NULL);
+
+    if (cnt != 0)
+    {
+        printf("Error! cnt=%d\n", cnt);
+    }
+    else
+    {
+        printf("Correct! cnt=%d\n", cnt);
+    }
+    sem_destroy(&mutex);
+    exit(0);
+}
\ No newline at end of file
diff --git a/exp1/task61 b/exp1/task61
new file mode 100755
index 0000000..1b8468a
Binary files /dev/null and b/exp1/task61 differ
diff --git a/exp1/task61.c b/exp1/task61.c
new file mode 100644
index 0000000..67dee6d
--- /dev/null
+++ b/exp1/task61.c
@@ -0,0 +1,53 @@
+#include <pthread.h>
+#include <time.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+void *wokerT1(void *vargp)
+{
+    for(int i=0; i<5; i++)
+    {
+        printf("My name is Lvjinzhong\n");
+        int sleep_time = rand() % 5 + 1;
+        sleep(sleep_time);
+    }
+    return NULL;
+}
+
+void *wokerT2(void *vargp)
+{
+    for(int i=0; i<5; i++)
+    {
+        printf("My student number is 2024414290124\n");
+        int sleep_time = rand() % 5 + 1;
+        sleep(sleep_time);
+    }
+    return NULL;
+}
+
+void *wokerT3(void *vargp)
+{
+    for(int i=0; i<5; i++)
+    {
+        time_t t = time(NULL);
+        printf("Current time %s\n",ctime(&t));
+        int sleep_time = rand() % 5 + 1;
+        sleep(sleep_time);
+    }
+    return NULL;
+}
+
+int main()
+{
+    pthread_t t1,t2,t3;
+    pthread_create(&t1, NULL, wokerT1, NULL);
+    pthread_create(&t2, NULL, wokerT2, NULL);
+    pthread_create(&t3, NULL, wokerT3, NULL);
+    
+    
+    pthread_join(t1, NULL);
+    pthread_join(t2, NULL);
+    pthread_join(t3, NULL);
+    return 0;
+}
\ No newline at end of file
diff --git a/吕锦中202441429012406/2024414290124-吕锦中-lab6.tar.gz b/吕锦中202441429012406/2024414290124-吕锦中-lab6.tar.gz
new file mode 100644
index 0000000..81e1f2f
Binary files /dev/null and b/吕锦中202441429012406/2024414290124-吕锦中-lab6.tar.gz differ
diff --git a/吕锦中202441429012406/badcount.c b/吕锦中202441429012406/badcount.c
new file mode 100644
index 0000000..5a10fe9
--- /dev/null
+++ b/吕锦中202441429012406/badcount.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+
+volatile long long counter = 0;
+long long niters;
+
+void *thread_func(void *arg) {
+    for (long long i = 0; i < niters; i++) {
+        counter++;
+    }
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <niters>\n", argv[0]);
+        return 1;
+    }
+    niters = atoll(argv[1]);
+
+    pthread_t t1, t2;
+    pthread_create(&t1, NULL, thread_func, NULL);
+    pthread_create(&t2, NULL, thread_func, NULL);
+
+    pthread_join(t1, NULL);
+    pthread_join(t2, NULL);
+
+    printf("Expected: %lld, Got: %lld\n", 2 * niters, counter);
+    if (counter != 2 * niters) {
+        printf("ERROR: Race condition detected!\n");
+    }
+    return 0;
+}
diff --git a/吕锦中202441429012406/matmult.c b/吕锦中202441429012406/matmult.c
new file mode 100644
index 0000000..fff4cb7
--- /dev/null
+++ b/吕锦中202441429012406/matmult.c
@@ -0,0 +1,145 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <sys/time.h>
+#include <string.h>
+
+#define MAX_THREADS 64
+
+int N;
+double **A, **B, **C_parallel, **C_serial;
+int nthreads;
+int rows_per_thread;
+
+void **allocate_matrix(int n) {
+    double **mat = (double **)malloc(n * sizeof(double *));
+    for (int i = 0; i < n; i++) {
+        mat[i] = (double *)malloc(n * sizeof(double));
+    }
+    return (void **)mat;
+}
+
+void free_matrix(double **mat, int n) {
+    for (int i = 0; i < n; i++) free(mat[i]);
+    free(mat);
+}
+
+void init_matrix(double **mat, int n) {
+    for (int i = 0; i < n; i++)
+        for (int j = 0; j < n; j++)
+            mat[i][j] = (double)(rand() % 100) / 10.0;
+}
+
+void *multiply_thread(void *arg) {
+    int start_row = *(int *)arg;
+    int end_row = start_row + rows_per_thread;
+    if (end_row > N) end_row = N;
+
+    for (int i = start_row; i < end_row; i++) {
+        for (int j = 0; j < N; j++) {
+            double sum = 0.0;
+            for (int k = 0; k < N; k++) {
+                sum += A[i][k] * B[k][j];
+            }
+            C_parallel[i][j] = sum;
+        }
+    }
+    return NULL;
+}
+
+void serial_multiply() {
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++) {
+            double sum = 0.0;
+            for (int k = 0; k < N; k++) {
+                sum += A[i][k] * B[k][j];
+            }
+            C_serial[i][j] = sum;
+        }
+    }
+}
+
+double get_time() {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec / 1000000.0;
+}
+
+int verify() {
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++) {
+            if (C_parallel[i][j] - C_serial[i][j] > 0.001 ||
+                C_serial[i][j] - C_parallel[i][j] > 0.001) {
+                printf("Mismatch at [%d][%d]: parallel=%.6f, serial=%.6f\n",
+                       i, j, C_parallel[i][j], C_serial[i][j]);
+                return 0;
+            }
+        }
+    }
+    return 1;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+        fprintf(stderr, "Usage: %s <N> <num_threads>\n", argv[0]);
+        return 1;
+    }
+
+    N = atoi(argv[1]);
+    nthreads = atoi(argv[2]);
+    if (nthreads > MAX_THREADS) nthreads = MAX_THREADS;
+    if (nthreads > N) nthreads = N;
+
+    rows_per_thread = N / nthreads;
+
+    srand(42);
+
+    A = (double **)allocate_matrix(N);
+    B = (double **)allocate_matrix(N);
+    C_parallel = (double **)allocate_matrix(N);
+    C_serial = (double **)allocate_matrix(N);
+
+    init_matrix(A, N);
+    init_matrix(B, N);
+
+    pthread_t threads[MAX_THREADS];
+    int starts[MAX_THREADS];
+
+    double t_start = get_time();
+
+    for (int i = 0; i < nthreads; i++) {
+        starts[i] = i * rows_per_thread;
+        pthread_create(&threads[i], NULL, multiply_thread, &starts[i]);
+    }
+    for (int i = 0; i < nthreads; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    double t_end = get_time();
+    double t_parallel = t_end - t_start;
+
+    /* Serial version for verification */
+    t_start = get_time();
+    serial_multiply();
+    t_end = get_time();
+    double t_serial = t_end - t_start;
+
+    printf("Matrix size: %d x %d, Threads: %d\n", N, N, nthreads);
+    printf("Parallel time: %.6f s\n", t_parallel);
+    printf("Serial time:   %.6f s\n", t_serial);
+    printf("Speedup: %.4f\n", t_serial / t_parallel);
+    printf("Efficiency: %.4f\n", t_serial / t_parallel / nthreads);
+
+    if (verify()) {
+        printf("Verification: SUCCESS\n");
+    } else {
+        printf("Verification: FAILED\n");
+    }
+
+    free_matrix(A, N);
+    free_matrix(B, N);
+    free_matrix(C_parallel, N);
+    free_matrix(C_serial, N);
+
+    return 0;
+}
diff --git a/吕锦中202441429012406/psum64.c b/吕锦中202441429012406/psum64.c
new file mode 100644
index 0000000..afcf8fe
--- /dev/null
+++ b/吕锦中202441429012406/psum64.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <sys/time.h>
+
+#define MAX_THREADS 64
+#define N 1000000000LL
+
+long long global_sum = 0;
+long long nelems_per_thread;
+pthread_mutex_t mutex;
+
+void *sum_thread(void *arg) {
+    long long start = *(long long *)arg;
+    long long local_sum = 0;
+    long long end = start + nelems_per_thread;
+    if (end > N) end = N;
+    for (long long i = start; i < end; i++) {
+        local_sum += i;
+    }
+    pthread_mutex_lock(&mutex);
+    global_sum += local_sum;
+    pthread_mutex_unlock(&mutex);
+    return NULL;
+}
+
+double get_time() {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec / 1000000.0;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <num_threads>\n", argv[0]);
+        return 1;
+    }
+
+    int nthreads = atoi(argv[1]);
+    if (nthreads > MAX_THREADS) nthreads = MAX_THREADS;
+
+    nelems_per_thread = N / nthreads;
+    pthread_mutex_init(&mutex, NULL);
+
+    pthread_t threads[MAX_THREADS];
+    long long starts[MAX_THREADS];
+
+    double t_start = get_time();
+
+    for (int i = 0; i < nthreads; i++) {
+        starts[i] = i * nelems_per_thread;
+        pthread_create(&threads[i], NULL, sum_thread, &starts[i]);
+    }
+
+    for (int i = 0; i < nthreads; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    double t_end = get_time();
+    double elapsed = t_end - t_start;
+
+    printf("Threads: %d, Sum: %lld, Time: %.6f s\n", nthreads, global_sum, elapsed);
+
+    pthread_mutex_destroy(&mutex);
+    return 0;
+}
diff --git a/吕锦中202441429012406/task61.c b/吕锦中202441429012406/task61.c
new file mode 100644
index 0000000..93b86d7
--- /dev/null
+++ b/吕锦中202441429012406/task61.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <time.h>
+#include <unistd.h>
+
+void *thread_T1(void *arg) {
+    for (int i = 1; i <= 5; i++) {
+        printf("My name is 吕锦中\n");
+        if (i < 5) {
+            int sleep_time = rand() % 5 + 1;
+            sleep(sleep_time);
+        }
+    }
+    return NULL;
+}
+
+void *thread_T2(void *arg) {
+    for (int i = 1; i <= 5; i++) {
+        printf("My student number is 2024414290124\n");
+        if (i < 5) {
+            int sleep_time = rand() % 5 + 1;
+            sleep(sleep_time);
+        }
+    }
+    return NULL;
+}
+
+void *thread_T3(void *arg) {
+    for (int i = 1; i <= 5; i++) {
+        time_t now = time(NULL);
+        struct tm *tm_info = localtime(&now);
+        char time_str[64];
+        strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M:%S", tm_info);
+        printf("Current time %s\n", time_str);
+        if (i < 5) {
+            int sleep_time = rand() % 5 + 1;
+            sleep(sleep_time);
+        }
+    }
+    return NULL;
+}
+
+int main() {
+    srand(time(NULL));
+    pthread_t t1, t2, t3;
+
+    pthread_create(&t1, NULL, thread_T1, NULL);
+    pthread_create(&t2, NULL, thread_T2, NULL);
+    pthread_create(&t3, NULL, thread_T3, NULL);
+
+    pthread_join(t1, NULL);
+    pthread_join(t2, NULL);
+    pthread_join(t3, NULL);
+
+    printf("All threads finished.\n");
+    return 0;
+}
diff --git a/吕锦中202441429012406/task62.c b/吕锦中202441429012406/task62.c
new file mode 100644
index 0000000..be4caa5
--- /dev/null
+++ b/吕锦中202441429012406/task62.c
@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+
+long long counter = 0;
+long long niters;
+sem_t mutex;
+
+void *thread_func(void *arg) {
+    for (long long i = 0; i < niters; i++) {
+        sem_wait(&mutex);
+        counter++;
+        sem_post(&mutex);
+    }
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <niters>\n", argv[0]);
+        return 1;
+    }
+    niters = atoll(argv[1]);
+
+    sem_init(&mutex, 0, 1);
+
+    pthread_t t1, t2;
+    pthread_create(&t1, NULL, thread_func, NULL);
+    pthread_create(&t2, NULL, thread_func, NULL);
+
+    pthread_join(t1, NULL);
+    pthread_join(t2, NULL);
+
+    sem_destroy(&mutex);
+
+    printf("Expected: %lld, Got: %lld\n", 2 * niters, counter);
+    if (counter == 2 * niters) {
+        printf("SUCCESS: No race condition.\n");
+    } else {
+        printf("ERROR: Race condition detected!\n");
+    }
+    return 0;
+}
diff --git a/吕锦中202441429012406/task63.c b/吕锦中202441429012406/task63.c
new file mode 100644
index 0000000..9f1ad48
--- /dev/null
+++ b/吕锦中202441429012406/task63.c
@@ -0,0 +1,176 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <time.h>
+#include <unistd.h>
+
+#define POISON -1
+
+typedef struct {
+    int *buf;
+    int n;
+    int outpos;
+    int inpos;
+    sem_t mutex;
+    sem_t slots;
+    sem_t items;
+} sbuf_t;
+
+long long produced_sum = 0;
+long long consumed_sum = 0;
+sem_t sum_mutex;
+int consumed_count = 0;
+int total_items;
+sem_t count_mutex;
+
+void sbuf_init(sbuf_t *sp, int n) {
+    sp->buf = (int *)malloc(n * sizeof(int));
+    sp->n = n;
+    sp->outpos = 0;
+    sp->inpos = 0;
+    sem_init(&sp->mutex, 0, 1);
+    sem_init(&sp->slots, 0, n);
+    sem_init(&sp->items, 0, 0);
+}
+
+void sbuf_deinit(sbuf_t *sp) {
+    free(sp->buf);
+    sem_destroy(&sp->mutex);
+    sem_destroy(&sp->slots);
+    sem_destroy(&sp->items);
+}
+
+void sbuf_insert(sbuf_t *sp, int item) {
+    sem_wait(&sp->slots);
+    sem_wait(&sp->mutex);
+    sp->buf[sp->inpos] = item;
+    sp->inpos = (sp->inpos + 1) % sp->n;
+    sem_post(&sp->mutex);
+    sem_post(&sp->items);
+}
+
+int sbuf_remove(sbuf_t *sp) {
+    sem_wait(&sp->items);
+    sem_wait(&sp->mutex);
+    int item = sp->buf[sp->outpos];
+    sp->outpos = (sp->outpos + 1) % sp->n;
+    sem_post(&sp->mutex);
+    sem_post(&sp->slots);
+    return item;
+}
+
+typedef struct {
+    sbuf_t *sp;
+    int num_items;
+    int id;
+} producer_arg_t;
+
+typedef struct {
+    sbuf_t *sp;
+    int id;
+} consumer_arg_t;
+
+void *producer(void *arg) {
+    producer_arg_t *pa = (producer_arg_t *)arg;
+    for (int i = 0; i < pa->num_items; i++) {
+        int val = rand() % 1000;
+        sbuf_insert(pa->sp, val);
+        sem_wait(&sum_mutex);
+        produced_sum += val;
+        sem_post(&sum_mutex);
+        printf("[Producer %d] produced %d\n", pa->id, val);
+    }
+    return NULL;
+}
+
+void *consumer(void *arg) {
+    consumer_arg_t *ca = (consumer_arg_t *)arg;
+    while (1) {
+        int item = sbuf_remove(ca->sp);
+        if (item == POISON) {
+            /* Put poison back for other consumers, then exit */
+            sbuf_insert(ca->sp, POISON);
+            break;
+        }
+        sem_wait(&sum_mutex);
+        consumed_sum += item;
+        sem_post(&sum_mutex);
+        sem_wait(&count_mutex);
+        consumed_count++;
+        sem_post(&count_mutex);
+        printf("[Consumer %d] consumed %d\n", ca->id, item);
+    }
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 5) {
+        fprintf(stderr, "Usage: %s <k_producers> <items_per_producer> <m_consumers> <N_buffer>\n", argv[0]);
+        return 1;
+    }
+
+    int k = atoi(argv[1]);
+    int items_per_producer = atoi(argv[2]);
+    int m = atoi(argv[3]);
+    int N = atoi(argv[4]);
+    total_items = k * items_per_producer;
+
+    srand(time(NULL));
+    sem_init(&sum_mutex, 0, 1);
+    sem_init(&count_mutex, 0, 1);
+
+    sbuf_t buf;
+    sbuf_init(&buf, N);
+
+    pthread_t *producers = malloc(k * sizeof(pthread_t));
+    pthread_t *consumers = malloc(m * sizeof(pthread_t));
+    producer_arg_t *pargs = malloc(k * sizeof(producer_arg_t));
+    consumer_arg_t *cargs = malloc(m * sizeof(consumer_arg_t));
+
+    for (int i = 0; i < k; i++) {
+        pargs[i].sp = &buf;
+        pargs[i].num_items = items_per_producer;
+        pargs[i].id = i + 1;
+        pthread_create(&producers[i], NULL, producer, &pargs[i]);
+    }
+
+    for (int i = 0; i < m; i++) {
+        cargs[i].sp = &buf;
+        cargs[i].id = i + 1;
+        pthread_create(&consumers[i], NULL, consumer, &cargs[i]);
+    }
+
+    /* Wait for all producers to finish */
+    for (int i = 0; i < k; i++) {
+        pthread_join(producers[i], NULL);
+    }
+
+    /* Insert one poison pill to start the termination chain */
+    sbuf_insert(&buf, POISON);
+
+    /* Wait for all consumers to finish */
+    for (int i = 0; i < m; i++) {
+        pthread_join(consumers[i], NULL);
+    }
+
+    printf("\n=== Verification ===\n");
+    printf("Produced sum : %lld\n", produced_sum);
+    printf("Consumed sum : %lld\n", consumed_sum);
+    if (produced_sum == consumed_sum) {
+        printf("SUCCESS: Sums match! Program is correct.\n");
+    } else {
+        printf("ERROR: Sum mismatch! Difference = %lld\n",
+               produced_sum - consumed_sum);
+    }
+
+    free(producers);
+    free(consumers);
+    free(pargs);
+    free(cargs);
+    sbuf_deinit(&buf);
+    sem_destroy(&sum_mutex);
+    sem_destroy(&count_mutex);
+
+    return 0;
+}
diff --git a/吕锦中202441429012406/task64.c b/吕锦中202441429012406/task64.c
new file mode 100644
index 0000000..4d1978d
--- /dev/null
+++ b/吕锦中202441429012406/task64.c
@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <sys/time.h>
+#include <math.h>
+
+#define MAX_THREADS 64
+#define N 1000000000LL
+
+long long global_sum = 0;
+long long nelems_per_thread;
+pthread_mutex_t mutex;
+
+void *sum_squares_thread(void *arg) {
+    long long start = *(long long *)arg;
+    long long end = start + nelems_per_thread;
+    if (end > N) end = N;
+    long long local_sum = 0;
+    for (long long i = start; i < end; i++) {
+        local_sum += i * i;
+    }
+    pthread_mutex_lock(&mutex);
+    global_sum += local_sum;
+    pthread_mutex_unlock(&mutex);
+    return NULL;
+}
+
+double get_time() {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec / 1000000.0;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <num_threads>\n", argv[0]);
+        return 1;
+    }
+
+    int nthreads = atoi(argv[1]);
+    if (nthreads > MAX_THREADS) nthreads = MAX_THREADS;
+
+    nelems_per_thread = N / nthreads;
+    pthread_mutex_init(&mutex, NULL);
+
+    pthread_t threads[MAX_THREADS];
+    long long starts[MAX_THREADS];
+
+    double t_start = get_time();
+
+    for (int i = 0; i < nthreads; i++) {
+        starts[i] = i * nelems_per_thread;
+        pthread_create(&threads[i], NULL, sum_squares_thread, &starts[i]);
+    }
+
+    for (int i = 0; i < nthreads; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    double t_end = get_time();
+    double elapsed = t_end - t_start;
+
+    /* Expected sum of squares: (n-1)*n*(2n-1)/6 */
+    long long expected = (N - 1) * N * (2 * N - 1) / 6;
+    printf("Threads: %d, Sum of squares: %lld, Expected: %lld, Time: %.6f s\n",
+           nthreads, global_sum, expected, elapsed);
+
+    pthread_mutex_destroy(&mutex);
+    return 0;
+}
diff --git a/吕锦中202441429012406/task66.c b/吕锦中202441429012406/task66.c
new file mode 100644
index 0000000..79a8bdf
--- /dev/null
+++ b/吕锦中202441429012406/task66.c
@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#define ITERATIONS 10000
+
+double get_time() {
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    return tv.tv_sec + tv.tv_usec / 1000000.0;
+}
+
+void *dummy_thread(void *arg) {
+    return NULL;
+}
+
+int main() {
+    double t_start, t_end;
+    double fork_total = 0, pthread_total = 0;
+
+    /* Measure fork() */
+    t_start = get_time();
+    for (int i = 0; i < ITERATIONS; i++) {
+        pid_t pid = fork();
+        if (pid == 0) {
+            _exit(0);
+        } else if (pid > 0) {
+            waitpid(pid, NULL, 0);
+        }
+    }
+    t_end = get_time();
+    fork_total = t_end - t_start;
+
+    /* Measure pthread_create() */
+    t_start = get_time();
+    for (int i = 0; i < ITERATIONS; i++) {
+        pthread_t tid;
+        pthread_create(&tid, NULL, dummy_thread, NULL);
+        pthread_join(tid, NULL);
+    }
+    t_end = get_time();
+    pthread_total = t_end - t_start;
+
+    printf("=== Performance Comparison ===\n");
+    printf("Iterations: %d\n", ITERATIONS);
+    printf("fork() total time:           %.6f s (avg: %.3f us)\n",
+           fork_total, fork_total / ITERATIONS * 1000000);
+    printf("pthread_create() total time: %.6f s (avg: %.3f us)\n",
+           pthread_total, pthread_total / ITERATIONS * 1000000);
+    printf("Ratio (fork/pthread): %.2fx\n", fork_total / pthread_total);
+    printf("\nExplanation: fork() creates a new process with a copy of the\n");
+    printf("entire address space, which is much heavier than pthread_create()\n");
+    printf("which only creates a new thread sharing the same address space.\n");
+
+    return 0;
+}
diff --git a/吕锦中202441429012406/task67.c b/吕锦中202441429012406/task67.c
new file mode 100644
index 0000000..6264274
--- /dev/null
+++ b/吕锦中202441429012406/task67.c
@@ -0,0 +1,177 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <string.h>
+#include <unistd.h>
+
+typedef struct {
+    int *buf;
+    int n;
+    int outpos;
+    int inpos;
+    sem_t mutex;
+    sem_t slots;
+    sem_t items;
+} sbuf_t;
+
+int num_workers = 5;
+int target_workers = 5;
+pthread_mutex_t worker_mutex = PTHREAD_MUTEX_INITIALIZER;
+pthread_t *workers = NULL;
+sbuf_t *sbuf_ptr = NULL;
+volatile int running = 1;
+
+void sbuf_init(sbuf_t *sp, int n) {
+    sp->buf = (int *)malloc(n * sizeof(int));
+    sp->n = n;
+    sp->outpos = 0;
+    sp->inpos = 0;
+    sem_init(&sp->mutex, 0, 1);
+    sem_init(&sp->slots, 0, n);
+    sem_init(&sp->items, 0, 0);
+}
+
+void sbuf_deinit(sbuf_t *sp) {
+    free(sp->buf);
+    sem_destroy(&sp->mutex);
+    sem_destroy(&sp->slots);
+    sem_destroy(&sp->items);
+}
+
+void sbuf_insert(sbuf_t *sp, int item) {
+    sem_wait(&sp->slots);
+    sem_wait(&sp->mutex);
+    sp->buf[sp->inpos] = item;
+    sp->inpos = (sp->inpos + 1) % sp->n;
+    sem_post(&sp->mutex);
+    sem_post(&sp->items);
+}
+
+int sbuf_remove(sbuf_t *sp) {
+    sem_wait(&sp->items);
+    sem_wait(&sp->mutex);
+    int item = sp->buf[sp->outpos];
+    sp->outpos = (sp->outpos + 1) % sp->n;
+    sem_post(&sp->mutex);
+    sem_post(&sp->slots);
+    return item;
+}
+
+void *worker_thread(void *arg) {
+    int id = *(int *)arg;
+    free(arg);
+    sbuf_t *sp = sbuf_ptr;
+
+    while (running) {
+        int seconds = sbuf_remove(sp);
+        if (seconds == -1) break;
+        printf("[Worker %d] executing task: sleep %d seconds\n", id, seconds);
+        sleep(seconds);
+        printf("[Worker %d] task completed\n", id);
+    }
+    return NULL;
+}
+
+void adjust_workers() {
+    pthread_mutex_lock(&worker_mutex);
+    int current = num_workers;
+    int target = target_workers;
+
+    if (target > current) {
+        /* Increase workers */
+        workers = realloc(workers, target * sizeof(pthread_t));
+        for (int i = current; i < target; i++) {
+            int *id = malloc(sizeof(int));
+            *id = i + 1;
+            pthread_create(&workers[i], NULL, worker_thread, id);
+        }
+        num_workers = target;
+    } else if (target < current) {
+        /* Decrease workers - insert poison pills */
+        int to_remove = current - target;
+        for (int i = 0; i < to_remove; i++) {
+            sbuf_insert(sbuf_ptr, -1);
+        }
+        for (int i = target; i < current; i++) {
+            pthread_join(workers[i], NULL);
+        }
+        num_workers = target;
+    }
+    pthread_mutex_unlock(&worker_mutex);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <buffer_size>\n", argv[0]);
+        return 1;
+    }
+
+    int buf_size = atoi(argv[1]);
+    sbuf_t buf;
+    sbuf_ptr = &buf;
+    sbuf_init(&buf, buf_size);
+
+    /* Create initial 5 workers */
+    workers = malloc(5 * sizeof(pthread_t));
+    for (int i = 0; i < 5; i++) {
+        int *id = malloc(sizeof(int));
+        *id = i + 1;
+        pthread_create(&workers[i], NULL, worker_thread, id);
+    }
+
+    printf("=== Dynamic Thread Pool ===\n");
+    printf("Commands:\n");
+    printf("  <task_count> <seconds>  - Add tasks\n");
+    printf("  quit                    - Exit\n");
+    printf("Initial workers: %d, Buffer size: %d\n\n", num_workers, buf_size);
+
+    char line[256];
+    while (1) {
+        printf("> ");
+        fflush(stdout);
+        if (!fgets(line, sizeof(line), stdin)) break;
+
+        if (strncmp(line, "quit", 4) == 0) break;
+
+        int task_count, seconds;
+        if (sscanf(line, "%d %d", &task_count, &seconds) == 2) {
+            printf("Adding %d tasks, each %d seconds...\n", task_count, seconds);
+
+            for (int i = 0; i < task_count; i++) {
+                /* Check if buffer is full - double workers */
+                int slots_avail;
+                sem_getvalue(&buf.slots, &slots_avail);
+                if (slots_avail == 0) {
+                    target_workers = num_workers * 2;
+                    printf("Buffer full, doubling workers to %d\n", target_workers);
+                    adjust_workers();
+                }
+
+                sbuf_insert(&buf, seconds);
+
+                /* Check if buffer is empty - halve workers */
+                int items_avail;
+                sem_getvalue(&buf.items, &items_avail);
+                if (items_avail == 0 && num_workers > 2) {
+                    target_workers = num_workers / 2;
+                    if (target_workers < 2) target_workers = 2;
+                    printf("Buffer empty, halving workers to %d\n", target_workers);
+                    adjust_workers();
+                }
+            }
+        } else {
+            printf("Invalid command. Usage: <task_count> <seconds>\n");
+        }
+    }
+
+    /* Shutdown */
+    running = 0;
+    target_workers = 0;
+    adjust_workers();
+
+    sbuf_deinit(&buf);
+    free(workers);
+    printf("Done.\n");
+    return 0;
+}