store Linux thread identifier in TLS and use it

Summary:
Linux thread identifier is something that we can get with `gettid`.
http://man7.org/linux/man-pages/man2/gettid.2.html

This TID is super usefully for providing thread information while debugging on Linux (this is
the thing that `ps` command uses, or procfs), but is not really mappable from
`std::thread::id` (e.g. the thread handle we get with `pthread_self()`).

Reviewed By: yfeldblum

Differential Revision: D19134596

fbshipit-source-id: 32ad025c5e378e3c7b55da1aad8dd9f3e26d0892

folly/SingletonThreadLocal.h

@@ -201,6 +201,10 @@ class SingletonThreadLocal {
       std::thread::id getThreadId() const {
         return this->base().getThreadId();
       }
+
+      uint64_t getOSThreadId() const {
+        return this->base().getOSThreadId();
+      }
     };
 
     Accessor(const Accessor&) = delete;

folly/ThreadLocal.h

@@ -373,6 +373,10 @@ class ThreadLocalPtr {
       std::thread::id getThreadId() const {
         return e_->getThreadEntry()->tid();
       }
+
+      uint64_t getOSThreadId() const {
+        return e_->getThreadEntry()->tid_os;
+      }
     };
 
     ~Accessor() {

folly/detail/ThreadLocalDetail.h

@@ -37,6 +37,7 @@
 #include <folly/memory/Malloc.h>
 #include <folly/portability/PThread.h>
 #include <folly/synchronization/MicroSpinLock.h>
+#include <folly/system/ThreadId.h>
 
 #include <folly/detail/StaticSingletonManager.h>
 
@@ -214,6 +215,7 @@ struct ThreadEntry {
   ThreadEntry* listNext{nullptr};
   StaticMetaBase* meta{nullptr};
   bool removed_{false};
+  uint64_t tid_os{};
   aligned_storage_for_t<std::thread::id> tid_data{};
 
   size_t getElementsCapacity() const noexcept {
@@ -480,6 +482,7 @@ struct StaticMeta final : StaticMetaBase {
       }
 
       threadEntry->tid() = std::this_thread::get_id();
+      threadEntry->tid_os = folly::getOSThreadID();
 
       // if we're adding a thread entry
       // we need to increment the list count

folly/io/async/Request.cpp

@@ -772,12 +772,12 @@ RequestContext::StaticContext& RequestContext::getStaticContext() {
   return SingletonT::get();
 }
 
-/* static */ std::vector<std::pair<std::thread::id, intptr_t>>
+/* static */ std::vector<RequestContext::RootIdInfo>
 RequestContext::getRootIdsFromAllThreads() {
-  std::vector<std::pair<std::thread::id, intptr_t>> result;
+  std::vector<RootIdInfo> result;
   auto accessor = SingletonT::accessAllThreads();
   for (auto it = accessor.begin(); it != accessor.end(); ++it) {
-    result.push_back({it.getThreadId(), it->second});
+    result.push_back({it->second, it.getThreadId(), it.getOSThreadId()});
   }
   return result;
 }

folly/io/async/Request.h

@@ -170,8 +170,12 @@ class RequestContext {
     return rootId_;
   }
 
-  static std::vector<std::pair<std::thread::id, intptr_t>>
-  getRootIdsFromAllThreads();
+  struct RootIdInfo {
+    intptr_t id;
+    std::thread::id tid;
+    uint64_t tidOS;
+  };
+  static std::vector<RootIdInfo> getRootIdsFromAllThreads();
 
   // The following APIs are used to add, remove and access RequestData instance
   // in the RequestContext instance, normally used for per-RequestContext

folly/io/async/test/RequestContextTest.cpp

@@ -77,7 +77,7 @@ class RequestContextTest : public ::testing::Test {
     std::vector<intptr_t> result;
     std::transform(
         rootids.begin(), rootids.end(), std::back_inserter(result), [](auto e) {
-          return e.second;
+          return e.id;
         });
     return result;
   }
@@ -373,7 +373,8 @@ TEST_F(RequestContextTest, ThreadId) {
   RequestContextScopeGuard g;
   auto ctxBase = std::make_shared<RequestContext>();
   auto rootids = RequestContext::getRootIdsFromAllThreads();
-  EXPECT_EQ(*folly::getThreadName(rootids[0].first), "DummyThread");
+  EXPECT_EQ(*folly::getThreadName(rootids[0].tid), "DummyThread");
+  EXPECT_EQ(rootids[0].tidOS, folly::getOSThreadID());
 
   EventBase base;
   base.runInEventBaseThread([&]() {
@@ -387,11 +388,11 @@ TEST_F(RequestContextTest, ThreadId) {
   th.join();
 
   std::sort(rootids.begin(), rootids.end(), [](const auto& a, const auto& b) {
-    auto aname = folly::getThreadName(a.first);
-    auto bname = folly::getThreadName(b.first);
+    auto aname = folly::getThreadName(a.tid);
+    auto bname = folly::getThreadName(b.tid);
     return (aname ? *aname : "zzz") < (bname ? *bname : "zzz");
   });
 
-  EXPECT_EQ(*folly::getThreadName(rootids[0].first), "DummyThread");
-  EXPECT_FALSE(folly::getThreadName(rootids[1].first));
+  EXPECT_EQ(*folly::getThreadName(rootids[0].tid), "DummyThread");
+  EXPECT_FALSE(folly::getThreadName(rootids[1].tid));
 }