Merge pull request MicrosoftDocs#3307 from AlexGuteniev/master

Mention limits of concurrency

Author: ktoliver

docs/standard-library/execution.md

@@ -1,7 +1,7 @@
 ---
 description: "Learn more about: <execution>"
 title: "<execution>"
-ms.date: "01/15/2021"
+ms.date: "08/17/2021"
 f1_keywords: ["<execution>", "execution/std::execution", "std::execution"]
 helpviewer_keywords: ["execution header"]
 ---
@@ -31,11 +31,15 @@ namespace std::execution {
 |[`parallel_unsequenced_policy` Class](parallel-unsequenced-policy-class.md)|Used as a unique type to disambiguate parallel algorithm overloading. Indicates that a parallel algorithm’s execution may be parallelized and vectorized.|
 |[`sequenced_policy` Class](sequenced-policy-class.md)|Used as a unique type to disambiguate parallel algorithm overloading. Specifies that a parallel algorithm’s execution may not be parallelized.|
 
+### Microsoft Specific
+ 
+When `parallel_policy` or `parallel_unsequenced_policy` cause the algorithm to be parallelized, the parallel execution uses Windows Thread Pool; see [Thread Pools](/windows/win32/procthread/thread-pools). The number of concurrent threads is limited to the thread pool default (currently 500). The number of threads concurrently executing on hardware is currently limited by the number of logical processors in the current process's processor group, so it is effectively limited to 64; see [Processor Groups](/windows/win32/procthread/processor-groups). The maximum number of chunks for data partitioning is also currently based on the number of logical processors in the current process's processor group.
+
 ## Requirements
 
 **Header:** \<execution>
 
-**Namespace:** stdext
+**Namespace:** std
 
 ## See also
 

docs/standard-library/future-functions.md

@@ -1,7 +1,7 @@
 ---
 description: "Learn more about: <future> functions"
 title: "<future> functions"
-ms.date: "11/04/2016"
+ms.date: "08/17/2021"
 f1_keywords: ["future/std::async", "future/std::future_category", "future/std::make_error_code", "future/std::make_error_condition", "future/std::swap"]
 ms.assetid: 1e3acc1e-736a-42dc-ade2-b2fe69aa96bc
 helpviewer_keywords: ["std::async [C++]", "std::future_category [C++]", "std::make_error_code [C++]", "std::make_error_condition [C++]", "std::swap [C++]"]
@@ -60,6 +60,10 @@ In all cases, the associated asynchronous state of the `future` object is not se
 
 The pseudo-function `INVOKE` is defined in [\<functional>](../standard-library/functional.md).
 
+### Microsoft Specific
+
+When the passed function is executed asynchronously, it is executed on Windows Thread Pool; see [Thread Pools](/windows/win32/procthread/thread-pools). The number of concurrent threads is limited to the thread pool default (currently 500). The number of threads concurrently executing on hardware is currently limited by the number of logical processor in the process's processor group, so it is effectively limited to 64; see [Processor Groups](/windows/win32/procthread/processor-groups).
+
 ## <a name="future_category"></a> future_category
 
 Returns a reference to the [error_category](../standard-library/error-category-class.md) object that characterizes errors that are associated with `future` objects.

docs/standard-library/thread-class.md

@@ -1,7 +1,7 @@
 ---
 description: "Learn more about: thread Class"
 title: "thread Class"
-ms.date: "11/04/2016"
+ms.date: "08/17/2021"
 f1_keywords: ["thread/std::thread", "thread/std::thread::id Class", "thread/std::thread::thread", "thread/std::thread::detach", "thread/std::thread::get_id", "thread/std::thread::hardware_concurrency", "thread/std::thread::join", "thread/std::thread::joinable", "thread/std::thread::native_handle", "thread/std::thread::swap"]
 ms.assetid: df249bc7-ff81-4ff9-a6d6-5e3d9a8f56a1
 helpviewer_keywords: ["std::thread [C++]", "std::thread [C++], thread", "std::thread [C++], detach", "std::thread [C++], get_id", "std::thread [C++], hardware_concurrency", "std::thread [C++], join", "std::thread [C++], joinable", "std::thread [C++], native_handle", "std::thread [C++], swap"]
@@ -100,6 +100,12 @@ static unsigned int hardware_concurrency() noexcept;
 
 An estimate of the number of hardware thread contexts. If the value cannot be computed or is not well defined, this method returns 0.
 
+### Microsoft Specific
+
+`hardware_concurrency` is currently defined to return the number of logical processors, which corresponds to the number of hardware threads that can execute simultaneously. It takes into account the number of physical processors, the number of cores in each physical processor, and simultaneous multithreading on each single core.
+ 
+However, on systems with more than 64 logical processors this number is capped by the number of logical processor in a single group; see [Processor Groups](/windows/win32/procthread/processor-groups).
+
 ## <a name="id_class"></a> thread::id Class
 
 Provides a unique identifier for each thread of execution in the process.