avoid lockup in ThreadPool::shutdown() on legacy host (yhirose#1417)

gh4ck3r · changbin-park · web-flow · commit ad7edc7b2798 · 2022-11-03T10:23:45.000-04:00
It is found on CentOS 7.0.1406 which is very early version of CentOS 7.

Co-authored-by: Changbin Park &lt;changbin.park@ahnlab.com&gt;
diff --git a/httplib.h b/httplib.h
@@ -560,10 +560,9 @@ class ThreadPool : public TaskQueue {
     {
       std::unique_lock<std::mutex> lock(mutex_);
       shutdown_ = true;
+      cond_.notify_all();
     }
 
-    cond_.notify_all();
-
     // Join...
     for (auto &t : threads_) {
       t.join();

Original file line number	Diff line number	Diff line change
`@@ -560,10 +560,9 @@ class ThreadPool : public TaskQueue {`
`560`	`560`	`{`
`561`	`561`	`std::unique_lock<std::mutex> lock(mutex_);`
`562`	`562`	`shutdown_ = true;`
	`563`	`+ cond_.notify_all();`
`563`	`564`	`}`
`564`	`565`
`565`		`- cond_.notify_all();`
`566`		`-`
`567`	`566`	`// Join...`
`568`	`567`	`for (auto &t : threads_) {`
`569`	`568`	`t.join();`