Use the multi-lockable form of std::lock for operator=

For = operators for lists that have mutexes, we were either
just taking the locks sequentially or hand-rolling a trick
to try to avoid lock inversion.  Use the std::lock mechanism
for this instead.

Differential Revision: https://reviews.llvm.org/D59957

llvm-svn: 357276

4 files changed, 16 insertions, 32 deletions

diff --git a/lldb/source/Breakpoint/BreakpointLocationCollection.cpp b/lldb/source/Breakpoint/BreakpointLocationCollection.cpp
index 413c12a06a6..0651ca09e8f 100644
--- a/lldb/source/Breakpoint/BreakpointLocationCollection.cpp
+++ b/lldb/source/Breakpoint/BreakpointLocationCollection.cpp
@@ -181,17 +181,11 @@ void BreakpointLocationCollection::GetDescription(
 
 BreakpointLocationCollection &BreakpointLocationCollection::operator=(
     const BreakpointLocationCollection &rhs) {
-  // Same trick as in ModuleList to avoid lock inversion.
   if (this != &rhs) {
-    if (uintptr_t(this) > uintptr_t(&rhs)) {
-      std::lock_guard<std::mutex> lhs_guard(m_collection_mutex);
-      std::lock_guard<std::mutex> rhs_guard(rhs.m_collection_mutex);
+      std::lock(m_collection_mutex, rhs.m_collection_mutex);
+      std::lock_guard<std::mutex> lhs_guard(m_collection_mutex, std::adopt_lock);
+      std::lock_guard<std::mutex> rhs_guard(rhs.m_collection_mutex, std::adopt_lock);
       m_break_loc_collection = rhs.m_break_loc_collection;
-    } else {
-      std::lock_guard<std::mutex> lhs_guard(m_collection_mutex);
-      std::lock_guard<std::mutex> rhs_guard(rhs.m_collection_mutex);
-      m_break_loc_collection = rhs.m_break_loc_collection;
-    }
   }
   return *this;
 }
diff --git a/lldb/source/Core/ModuleList.cpp b/lldb/source/Core/ModuleList.cpp
index 8740bd0f40a..d59e429ad9f 100644
--- a/lldb/source/Core/ModuleList.cpp
+++ b/lldb/source/Core/ModuleList.cpp
@@ -130,25 +130,12 @@ ModuleList::ModuleList(ModuleList::Notifier *notifier)
 
 const ModuleList &ModuleList::operator=(const ModuleList &rhs) {
   if (this != &rhs) {
-    // That's probably me nit-picking, but in theoretical situation:
-    //
-    // * that two threads A B and
-    // * two ModuleList's x y do opposite assignments ie.:
-    //
-    //  in thread A: | in thread B:
-    //    x = y;     |   y = x;
-    //
-    // This establishes correct(same) lock taking order and thus avoids
-    // priority inversion.
-    if (uintptr_t(this) > uintptr_t(&rhs)) {
-      std::lock_guard<std::recursive_mutex> lhs_guard(m_modules_mutex);
-      std::lock_guard<std::recursive_mutex> rhs_guard(rhs.m_modules_mutex);
-      m_modules = rhs.m_modules;
-    } else {
-      std::lock_guard<std::recursive_mutex> lhs_guard(m_modules_mutex);
-      std::lock_guard<std::recursive_mutex> rhs_guard(rhs.m_modules_mutex);
-      m_modules = rhs.m_modules;
-    }
+    std::lock(m_modules_mutex, rhs.m_modules_mutex);
+    std::lock_guard<std::recursive_mutex> lhs_guard(m_modules_mutex, 
+                                                    std::adopt_lock);
+    std::lock_guard<std::recursive_mutex> rhs_guard(rhs.m_modules_mutex, 
+                                                    std::adopt_lock);
+    m_modules = rhs.m_modules;
   }
   return *this;
 }
diff --git a/lldb/source/Target/SectionLoadList.cpp b/lldb/source/Target/SectionLoadList.cpp
index 45b6b52e184..598f49ca13d 100644
--- a/lldb/source/Target/SectionLoadList.cpp
+++ b/lldb/source/Target/SectionLoadList.cpp
@@ -27,8 +27,9 @@ SectionLoadList::SectionLoadList(const SectionLoadList &rhs)
 }
 
 void SectionLoadList::operator=(const SectionLoadList &rhs) {
-  std::lock_guard<std::recursive_mutex> lhs_guard(m_mutex);
-  std::lock_guard<std::recursive_mutex> rhs_guard(rhs.m_mutex);
+  std::lock(m_mutex, rhs.m_mutex);
+  std::lock_guard<std::recursive_mutex> lhs_guard(m_mutex, std::adopt_lock);
+  std::lock_guard<std::recursive_mutex> rhs_guard(rhs.m_mutex, std::adopt_lock);
   m_addr_to_sect = rhs.m_addr_to_sect;
   m_sect_to_addr = rhs.m_sect_to_addr;
 }
diff --git a/lldb/source/Target/ThreadList.cpp b/lldb/source/Target/ThreadList.cpp
index 86248da4993..afdfda3b0ae 100644
--- a/lldb/source/Target/ThreadList.cpp
+++ b/lldb/source/Target/ThreadList.cpp
@@ -37,8 +37,10 @@ const ThreadList &ThreadList::operator=(const ThreadList &rhs) {
   if (this != &rhs) {
     // Lock both mutexes to make sure neither side changes anyone on us while
     // the assignment occurs
-    std::lock_guard<std::recursive_mutex> guard(GetMutex());
-    std::lock_guard<std::recursive_mutex> rhs_guard(rhs.GetMutex());
+    std::lock(GetMutex(), rhs.GetMutex());
+    std::lock_guard<std::recursive_mutex> guard(GetMutex(), std::adopt_lock);
+    std::lock_guard<std::recursive_mutex> rhs_guard(rhs.GetMutex(), 
+                                                    std::adopt_lock);
 
     m_process = rhs.m_process;
     m_stop_id = rhs.m_stop_id;