book: typos fix in ch07-thread (changkun#118)

changdingfang · web-flow · commit 518c6e97d71b · 2020-08-28T17:24:05.000+02:00
revise the code to make sure it consistent with the book description
diff --git a/book/en-us/07-thread.md b/book/en-us/07-thread.md
@@ -429,7 +429,7 @@ In order to achieve the ultimate performance and achieve consistency of various
     std::atomic<int> counter = {0};
     std::vector<std::thread> vt;
     for (int i = 0; i < 100; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, std::memory_order_relaxed);
         });
     }
@@ -444,7 +444,8 @@ In order to achieve the ultimate performance and achieve consistency of various
 2. Release/consumption model: In this model, we begin to limit the order of operations between processes. If a thread needs to modify a value, but another thread will have a dependency on that operation of the value, that is, the latter depends. former. Specifically, thread A has completed three writes to `x`, and thread `B` relies only on the third `x` write operation, regardless of the first two write behaviors of `x`, then `A ` When active `x.release()` (ie using `std::memory_order_release`), the option `std::memory_order_consume` ensures that `B` observes `A` when calling `x.load()` Three writes to `x`. Let's look at an example:
 
     ```cpp
-    std::atomic<int*> ptr;
+    // initialize as nullptr to prevent consumer load a dangling pointer
+    std::atomic<int*> ptr(nullptr);
     int v;
     std::thread producer([&]() {
         int* p = new int(42);
@@ -500,7 +501,7 @@ In order to achieve the ultimate performance and achieve consistency of various
     std::atomic<int> counter = {0};
     std::vector<std::thread> vt;
     for (int i = 0; i < 100; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, std::memory_order_seq_cst);
         });
     }
diff --git a/book/zh-cn/07-thread.md b/book/zh-cn/07-thread.md
@@ -439,7 +439,7 @@ int main() {
     std::atomic<int> counter = {0};
     std::vector<std::thread> vt;
     for (int i = 0; i < 100; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, std::memory_order_relaxed);
         });
     }
@@ -453,7 +453,8 @@ int main() {
 2. 释放/消费模型：在此模型中，我们开始限制进程间的操作顺序，如果某个线程需要修改某个值，但另一个线程会对该值的某次操作产生依赖，即后者依赖前者。具体而言，线程 A 完成了三次对 `x` 的写操作，线程 `B` 仅依赖其中第三次 `x` 的写操作，与 `x` 的前两次写行为无关，则当 `A` 主动 `x.release()` 时候（即使用 `std::memory_order_release`），选项 `std::memory_order_consume` 能够确保 `B` 在调用 `x.load()` 时候观察到 `A` 中第三次对 `x` 的写操作。我们来看一个例子：
 
     ```cpp
-    std::atomic<int*> ptr;
+    // 初始化为 nullptr 防止 consumer 线程从野指针进行读取
+    std::atomic<int*> ptr(nullptr);
     int v;
     std::thread producer([&]() {
         int* p = new int(42);
@@ -509,7 +510,7 @@ int main() {
     std::atomic<int> counter = {0};
     std::vector<std::thread> vt;
     for (int i = 0; i < 100; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, std::memory_order_seq_cst);
         });
     }
diff --git a/code/7/7.8.memory.order.cpp b/code/7/7.8.memory.order.cpp
@@ -15,15 +15,15 @@
 using namespace std;
 using namespace std::chrono;
 
-atomic<int> counter = {0};
 const int N = 10000;
 
 void relaxed_order() {
     cout << "relaxed_order: " << endl;
 
+    atomic<int> counter = {0};
     vector<thread> vt;
     for (int i = 0; i < N; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, memory_order_relaxed);
         });
     }
@@ -86,9 +86,10 @@ void release_acquire_order() {
 void sequential_consistent_order() {
     cout << "sequential_consistent_order: " << endl;
 
+    atomic<int> counter = {0};
     vector<thread> vt;
     for (int i = 0; i < N; ++i) {
-        vt.emplace_back([](){
+        vt.emplace_back([&](){
             counter.fetch_add(1, memory_order_seq_cst);
         });
     }
