Refactor user/group name resolving code

Summary:
This creates an abstract base class called "UserIDResolver", which can
be implemented to provide user/group ID resolution capabilities for
various objects. Posix host implement a PosixUserIDResolver, which does
that using posix apis (getpwuid and friends).  PlatformGDBRemote
forwards queries over the gdb-remote link, etc. ProcessInstanceInfo
class is refactored to make use of this interface instead of taking a
platform pointer as an argument. The base resolver class already
implements caching and thread-safety, so implementations don't have to
worry about that.

The main motivating factor for this was to remove external dependencies
from the ProcessInstanceInfo class (so it can be put next to
ProcessLaunchInfo and friends), but it has other benefits too:
- ability to test the user name caching code
- ability to test ProcessInstanceInfo dumping code
- consistent interface for user/group resolution between Platform and
  Host classes.

Reviewers: zturner, clayborg, jingham

Subscribers: mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D58167

llvm-svn: 355323

11 files changed, 147 insertions, 167 deletions

diff --git a/lldb/source/Commands/CommandObjectPlatform.cpp b/lldb/source/Commands/CommandObjectPlatform.cpp
index c4aee060d7d..8bb88f965cf 100644
--- a/lldb/source/Commands/CommandObjectPlatform.cpp
+++ b/lldb/source/Commands/CommandObjectPlatform.cpp
@@ -1151,10 +1151,9 @@ protected:
           if (pid != LLDB_INVALID_PROCESS_ID) {
             ProcessInstanceInfo proc_info;
             if (platform_sp->GetProcessInfo(pid, proc_info)) {
-              ProcessInstanceInfo::DumpTableHeader(ostrm, platform_sp.get(),
-                                                   m_options.show_args,
+              ProcessInstanceInfo::DumpTableHeader(ostrm, m_options.show_args,
                                                    m_options.verbose);
-              proc_info.DumpAsTableRow(ostrm, platform_sp.get(),
+              proc_info.DumpAsTableRow(ostrm, platform_sp->GetUserIDResolver(),
                                        m_options.show_args, m_options.verbose);
               result.SetStatus(eReturnStatusSuccessFinishResult);
             } else {
@@ -1212,13 +1211,12 @@ protected:
                 result.AppendMessageWithFormat(" whose name %s \"%s\"",
                                                match_desc, match_name);
               result.AppendMessageWithFormat("\n");
-              ProcessInstanceInfo::DumpTableHeader(ostrm, platform_sp.get(),
-                                                   m_options.show_args,
+              ProcessInstanceInfo::DumpTableHeader(ostrm, m_options.show_args,
                                                    m_options.verbose);
               for (uint32_t i = 0; i < matches; ++i) {
                 proc_infos.GetProcessInfoAtIndex(i).DumpAsTableRow(
-                    ostrm, platform_sp.get(), m_options.show_args,
-                    m_options.verbose);
+                    ostrm, platform_sp->GetUserIDResolver(),
+                    m_options.show_args, m_options.verbose);
               }
             }
           }
@@ -1453,7 +1451,7 @@ protected:
               if (platform_sp->GetProcessInfo(pid, proc_info)) {
                 ostrm.Printf("Process information for process %" PRIu64 ":\n",
                              pid);
-                proc_info.Dump(ostrm, platform_sp.get());
+                proc_info.Dump(ostrm, platform_sp->GetUserIDResolver());
               } else {
                 ostrm.Printf("error: no process information is available for "
                              "process %" PRIu64 "\n",
diff --git a/lldb/source/Host/posix/HostInfoPosix.cpp b/lldb/source/Host/posix/HostInfoPosix.cpp
index 76f9cdbc4ed..864d6c9a252 100644
--- a/lldb/source/Host/posix/HostInfoPosix.cpp
+++ b/lldb/source/Host/posix/HostInfoPosix.cpp
@@ -48,40 +48,38 @@ bool HostInfoPosix::GetHostname(std::string &s) {
 #define USE_GETPWUID
 #endif
 
-#ifdef USE_GETPWUID
-static std::mutex s_getpwuid_lock;
-#endif
-
-const char *HostInfoPosix::LookupUserName(uint32_t uid,
-                                          std::string &user_name) {
+namespace {
+class PosixUserIDResolver : public UserIDResolver {
+protected:
+  llvm::Optional<std::string> DoGetUserName(id_t uid) override;
+  llvm::Optional<std::string> DoGetGroupName(id_t gid) override;
+};
+} // namespace
+
+llvm::Optional<std::string> PosixUserIDResolver::DoGetUserName(id_t uid) {
 #ifdef USE_GETPWUID
   // getpwuid_r is missing from android-9
-  // make getpwuid thread safe with a mutex
-  std::lock_guard<std::mutex> lock(s_getpwuid_lock);
+  // UserIDResolver provides some thread safety by making sure noone calls this
+  // function concurrently, but using getpwuid is ultimately not thread-safe as
+  // we don't know who else might be calling it.
   struct passwd *user_info_ptr = ::getpwuid(uid);
-  if (user_info_ptr) {
-    user_name.assign(user_info_ptr->pw_name);
-    return user_name.c_str();
-  }
+  if (user_info_ptr)
+    return std::string(user_info_ptr->pw_name);
 #else
   struct passwd user_info;
   struct passwd *user_info_ptr = &user_info;
   char user_buffer[PATH_MAX];
   size_t user_buffer_size = sizeof(user_buffer);
   if (::getpwuid_r(uid, &user_info, user_buffer, user_buffer_size,
-                   &user_info_ptr) == 0) {
-    if (user_info_ptr) {
-      user_name.assign(user_info_ptr->pw_name);
-      return user_name.c_str();
-    }
+                   &user_info_ptr) == 0 &&
+      user_info_ptr) {
+    return std::string(user_info_ptr->pw_name);
   }
 #endif
-  user_name.clear();
-  return nullptr;
+  return llvm::None;
 }
 
-const char *HostInfoPosix::LookupGroupName(uint32_t gid,
-                                           std::string &group_name) {
+llvm::Optional<std::string> PosixUserIDResolver::DoGetGroupName(id_t gid) {
 #ifndef __ANDROID__
   char group_buffer[PATH_MAX];
   size_t group_buffer_size = sizeof(group_buffer);
@@ -90,24 +88,25 @@ const char *HostInfoPosix::LookupGroupName(uint32_t gid,
   // Try the threadsafe version first
   if (::getgrgid_r(gid, &group_info, group_buffer, group_buffer_size,
                    &group_info_ptr) == 0) {
-    if (group_info_ptr) {
-      group_name.assign(group_info_ptr->gr_name);
-      return group_name.c_str();
-    }
+    if (group_info_ptr)
+      return std::string(group_info_ptr->gr_name);
   } else {
     // The threadsafe version isn't currently working for me on darwin, but the
     // non-threadsafe version is, so I am calling it below.
     group_info_ptr = ::getgrgid(gid);
-    if (group_info_ptr) {
-      group_name.assign(group_info_ptr->gr_name);
-      return group_name.c_str();
-    }
+    if (group_info_ptr)
+      return std::string(group_info_ptr->gr_name);
   }
-  group_name.clear();
 #else
   assert(false && "getgrgid_r() not supported on Android");
 #endif
-  return NULL;
+  return llvm::None;
+}
+
+static llvm::ManagedStatic<PosixUserIDResolver> g_user_id_resolver;
+
+UserIDResolver &HostInfoPosix::GetUserIDResolver() {
+  return *g_user_id_resolver;
 }
 
 uint32_t HostInfoPosix::GetUserID() { return getuid(); }
diff --git a/lldb/source/Plugins/Platform/Kalimba/PlatformKalimba.h b/lldb/source/Plugins/Platform/Kalimba/PlatformKalimba.h
index 2d395925bb1..880c3ae7057 100644
--- a/lldb/source/Plugins/Platform/Kalimba/PlatformKalimba.h
+++ b/lldb/source/Plugins/Platform/Kalimba/PlatformKalimba.h
@@ -62,6 +62,10 @@ public:
 
   void CalculateTrapHandlerSymbolNames() override;
 
+  UserIDResolver &GetUserIDResolver() override {
+    return UserIDResolver::GetNoopResolver();
+  }
+
 protected:
   lldb::PlatformSP m_remote_platform_sp;
 
diff --git a/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.cpp b/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.cpp
index cb971b02dcb..4ced723b0b2 100644
--- a/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.cpp
+++ b/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.cpp
@@ -340,29 +340,20 @@ const char *PlatformRemoteGDBServer::GetHostname() {
   return m_name.c_str();
 }
 
-const char *PlatformRemoteGDBServer::GetUserName(uint32_t uid) {
-  // Try and get a cache user name first
-  const char *cached_user_name = Platform::GetUserName(uid);
-  if (cached_user_name)
-    return cached_user_name;
+llvm::Optional<std::string>
+PlatformRemoteGDBServer::DoGetUserName(UserIDResolver::id_t uid) {
   std::string name;
   if (m_gdb_client.GetUserName(uid, name))
-    return SetCachedUserName(uid, name.c_str(), name.size());
-
-  SetUserNameNotFound(uid); // Negative cache so we don't keep sending packets
-  return NULL;
+    return std::move(name);
+  return llvm::None;
 }
 
-const char *PlatformRemoteGDBServer::GetGroupName(uint32_t gid) {
-  const char *cached_group_name = Platform::GetGroupName(gid);
-  if (cached_group_name)
-    return cached_group_name;
+llvm::Optional<std::string>
+PlatformRemoteGDBServer::DoGetGroupName(UserIDResolver::id_t gid) {
   std::string name;
   if (m_gdb_client.GetGroupName(gid, name))
-    return SetCachedGroupName(gid, name.c_str(), name.size());
-
-  SetGroupNameNotFound(gid); // Negative cache so we don't keep sending packets
-  return NULL;
+    return std::move(name);
+  return llvm::None;
 }
 
 uint32_t PlatformRemoteGDBServer::FindProcesses(
diff --git a/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.h b/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.h
index d7a5aa5537c..d67cfc2f5da 100644
--- a/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.h
+++ b/lldb/source/Plugins/Platform/gdb-server/PlatformRemoteGDBServer.h
@@ -19,7 +19,7 @@
 namespace lldb_private {
 namespace platform_gdb_server {
 
-class PlatformRemoteGDBServer : public Platform {
+class PlatformRemoteGDBServer : public Platform, private UserIDResolver {
 public:
   static void Initialize();
 
@@ -100,9 +100,7 @@ public:
   // name if connected.
   const char *GetHostname() override;
 
-  const char *GetUserName(uint32_t uid) override;
-
-  const char *GetGroupName(uint32_t gid) override;
+  UserIDResolver &GetUserIDResolver() override { return *this; }
 
   bool IsConnected() const override;
 
@@ -195,6 +193,9 @@ private:
                                const std::string &platform_hostname,
                                uint16_t port, const char *socket_name);
 
+  llvm::Optional<std::string> DoGetUserName(UserIDResolver::id_t uid) override;
+  llvm::Optional<std::string> DoGetGroupName(UserIDResolver::id_t uid) override;
+
   DISALLOW_COPY_AND_ASSIGN(PlatformRemoteGDBServer);
 };
 
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerCommon.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerCommon.cpp
index c7a4127d9d4..5bc0c25c587 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerCommon.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerCommon.cpp
@@ -436,10 +436,10 @@ GDBRemoteCommunicationServerCommon::Handle_qUserName(
   packet.SetFilePos(::strlen("qUserName:"));
   uint32_t uid = packet.GetU32(UINT32_MAX);
   if (uid != UINT32_MAX) {
-    std::string name;
-    if (HostInfo::LookupUserName(uid, name)) {
+    if (llvm::Optional<llvm::StringRef> name =
+            HostInfo::GetUserIDResolver().GetUserName(uid)) {
       StreamString response;
-      response.PutStringAsRawHex8(name);
+      response.PutStringAsRawHex8(*name);
       return SendPacketNoLock(response.GetString());
     }
   }
@@ -457,10 +457,10 @@ GDBRemoteCommunicationServerCommon::Handle_qGroupName(
   packet.SetFilePos(::strlen("qGroupName:"));
   uint32_t gid = packet.GetU32(UINT32_MAX);
   if (gid != UINT32_MAX) {
-    std::string name;
-    if (HostInfo::LookupGroupName(gid, name)) {
+    if (llvm::Optional<llvm::StringRef> name =
+            HostInfo::GetUserIDResolver().GetGroupName(gid)) {
       StreamString response;
-      response.PutStringAsRawHex8(name);
+      response.PutStringAsRawHex8(*name);
       return SendPacketNoLock(response.GetString());
     }
   }
diff --git a/lldb/source/Target/Platform.cpp b/lldb/source/Target/Platform.cpp
index a93913b25c8..b57c3523e72 100644
--- a/lldb/source/Target/Platform.cpp
+++ b/lldb/source/Target/Platform.cpp
@@ -384,10 +384,10 @@ Platform::Platform(bool is_host)
     : m_is_host(is_host), m_os_version_set_while_connected(false),
       m_system_arch_set_while_connected(false), m_sdk_sysroot(), m_sdk_build(),
       m_working_dir(), m_remote_url(), m_name(), m_system_arch(), m_mutex(),
-      m_uid_map(), m_gid_map(), m_max_uid_name_len(0), m_max_gid_name_len(0),
-      m_supports_rsync(false), m_rsync_opts(), m_rsync_prefix(),
-      m_supports_ssh(false), m_ssh_opts(), m_ignores_remote_hostname(false),
-      m_trap_handlers(), m_calculated_trap_handlers(false),
+      m_max_uid_name_len(0), m_max_gid_name_len(0), m_supports_rsync(false),
+      m_rsync_opts(), m_rsync_prefix(), m_supports_ssh(false), m_ssh_opts(),
+      m_ignores_remote_hostname(false), m_trap_handlers(),
+      m_calculated_trap_handlers(false),
       m_module_cache(llvm::make_unique<ModuleCache>()) {
   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_OBJECT));
   if (log)
@@ -834,34 +834,6 @@ bool Platform::SetRemoteWorkingDirectory(const FileSpec &working_dir) {
   return true;
 }
 
-const char *Platform::GetUserName(uint32_t uid) {
-#if !defined(LLDB_DISABLE_POSIX)
-  const char *user_name = GetCachedUserName(uid);
-  if (user_name)
-    return user_name;
-  if (IsHost()) {
-    std::string name;
-    if (HostInfo::LookupUserName(uid, name))
-      return SetCachedUserName(uid, name.c_str(), name.size());
-  }
-#endif
-  return nullptr;
-}
-
-const char *Platform::GetGroupName(uint32_t gid) {
-#if !defined(LLDB_DISABLE_POSIX)
-  const char *group_name = GetCachedGroupName(gid);
-  if (group_name)
-    return group_name;
-  if (IsHost()) {
-    std::string name;
-    if (HostInfo::LookupGroupName(gid, name))
-      return SetCachedGroupName(gid, name.c_str(), name.size());
-  }
-#endif
-  return nullptr;
-}
-
 bool Platform::SetOSVersion(llvm::VersionTuple version) {
   if (IsHost()) {
     // We don't need anyone setting the OS version for the host platform, we
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index 0e8b314917e..2723b698517 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -278,8 +278,7 @@ bool ProcessProperties::GetStopOnExec() const {
       nullptr, idx, g_properties[idx].default_uint_value != 0);
 }
 
-void ProcessInstanceInfo::Dump(Stream &s, Platform *platform) const {
-  const char *cstr;
+void ProcessInstanceInfo::Dump(Stream &s, UserIDResolver &resolver) const {
   if (m_pid != LLDB_INVALID_PROCESS_ID)
     s.Printf("    pid = %" PRIu64 "\n", m_pid);
 
@@ -311,26 +310,26 @@ void ProcessInstanceInfo::Dump(Stream &s, Platform *platform) const {
     s.EOL();
   }
 
-  if (m_uid != UINT32_MAX) {
-    cstr = platform->GetUserName(m_uid);
-    s.Printf("    uid = %-5u (%s)\n", m_uid, cstr ? cstr : "");
+  if (UserIDIsValid()) {
+    s.Format("    uid = {0,-5} ({1})\n", GetUserID(),
+             resolver.GetUserName(GetUserID()).getValueOr(""));
   }
-  if (m_gid != UINT32_MAX) {
-    cstr = platform->GetGroupName(m_gid);
-    s.Printf("    gid = %-5u (%s)\n", m_gid, cstr ? cstr : "");
+  if (GroupIDIsValid()) {
+    s.Format("    gid = {0,-5} ({1})\n", GetGroupID(),
+             resolver.GetGroupName(GetGroupID()).getValueOr(""));
   }
-  if (m_euid != UINT32_MAX) {
-    cstr = platform->GetUserName(m_euid);
-    s.Printf("   euid = %-5u (%s)\n", m_euid, cstr ? cstr : "");
+  if (EffectiveUserIDIsValid()) {
+    s.Format("   euid = {0,-5} ({1})\n", GetEffectiveUserID(),
+             resolver.GetUserName(GetEffectiveUserID()).getValueOr(""));
   }
-  if (m_egid != UINT32_MAX) {
-    cstr = platform->GetGroupName(m_egid);
-    s.Printf("   egid = %-5u (%s)\n", m_egid, cstr ? cstr : "");
+  if (EffectiveGroupIDIsValid()) {
+    s.Format("   egid = {0,-5} ({1})\n", GetEffectiveGroupID(),
+             resolver.GetGroupName(GetEffectiveGroupID()).getValueOr(""));
   }
 }
 
-void ProcessInstanceInfo::DumpTableHeader(Stream &s, Platform *platform,
-                                          bool show_args, bool verbose) {
+void ProcessInstanceInfo::DumpTableHeader(Stream &s, bool show_args,
+                                          bool verbose) {
   const char *label;
   if (show_args || verbose)
     label = "ARGUMENTS";
@@ -350,49 +349,33 @@ void ProcessInstanceInfo::DumpTableHeader(Stream &s, Platform *platform,
   }
 }
 
-void ProcessInstanceInfo::DumpAsTableRow(Stream &s, Platform *platform,
+void ProcessInstanceInfo::DumpAsTableRow(Stream &s, UserIDResolver &resolver,
                                          bool show_args, bool verbose) const {
   if (m_pid != LLDB_INVALID_PROCESS_ID) {
-    const char *cstr;
     s.Printf("%-6" PRIu64 " %-6" PRIu64 " ", m_pid, m_parent_pid);
 
     StreamString arch_strm;
     if (m_arch.IsValid())
       m_arch.DumpTriple(arch_strm);
 
-    if (verbose) {
-      cstr = platform->GetUserName(m_uid);
-      if (cstr &&
-          cstr[0]) // Watch for empty string that indicates lookup failed
-        s.Printf("%-10s ", cstr);
-      else
-        s.Printf("%-10u ", m_uid);
-
-      cstr = platform->GetGroupName(m_gid);
-      if (cstr &&
-          cstr[0]) // Watch for empty string that indicates lookup failed
-        s.Printf("%-10s ", cstr);
-      else
-        s.Printf("%-10u ", m_gid);
-
-      cstr = platform->GetUserName(m_euid);
-      if (cstr &&
-          cstr[0]) // Watch for empty string that indicates lookup failed
-        s.Printf("%-10s ", cstr);
-      else
-        s.Printf("%-10u ", m_euid);
-
-      cstr = platform->GetGroupName(m_egid);
-      if (cstr &&
-          cstr[0]) // Watch for empty string that indicates lookup failed
-        s.Printf("%-10s ", cstr);
+    auto print = [&](UserIDResolver::id_t id,
+                     llvm::Optional<llvm::StringRef> (UserIDResolver::*get)(
+                         UserIDResolver::id_t id)) {
+      if (auto name = (resolver.*get)(id))
+        s.Format("{0,-10} ", *name);
       else
-        s.Printf("%-10u ", m_egid);
+        s.Format("{0,-10} ", id);
+    };
+    if (verbose) {
+      print(m_uid, &UserIDResolver::GetUserName);
+      print(m_gid, &UserIDResolver::GetGroupName);
+      print(m_euid, &UserIDResolver::GetUserName);
+      print(m_egid, &UserIDResolver::GetGroupName);
 
       s.Printf("%-24s ", arch_strm.GetData());
     } else {
-      s.Printf("%-10s %-24s ", platform->GetUserName(m_euid),
-               arch_strm.GetData());
+      print(m_euid, &UserIDResolver::GetUserName);
+      s.Printf(" %-24s ", arch_strm.GetData());
     }
 
     if (verbose || show_args) {
@@ -3057,11 +3040,10 @@ Status Process::Attach(ProcessAttachInfo &attach_info) {
                 process_name, sizeof(process_name));
             if (num_matches > 1) {
               StreamString s;
-              ProcessInstanceInfo::DumpTableHeader(s, platform_sp.get(), true,
-                                                   false);
+              ProcessInstanceInfo::DumpTableHeader(s, true, false);
               for (size_t i = 0; i < num_matches; i++) {
                 process_infos.GetProcessInfoAtIndex(i).DumpAsTableRow(
-                    s, platform_sp.get(), true, false);
+                    s, platform_sp->GetUserIDResolver(), true, false);
               }
               error.SetErrorStringWithFormat(
                   "more than one process named %s:\n%s", process_name,
diff --git a/lldb/source/Target/RemoteAwarePlatform.cpp b/lldb/source/Target/RemoteAwarePlatform.cpp
index 04cb6cedccf..1704e1533e9 100644
--- a/lldb/source/Target/RemoteAwarePlatform.cpp
+++ b/lldb/source/Target/RemoteAwarePlatform.cpp
@@ -10,6 +10,7 @@
 #include "lldb/Host/FileCache.h"
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/Host.h"
+#include "lldb/Host/HostInfo.h"
 
 using namespace lldb_private;
 
@@ -204,25 +205,12 @@ const char *RemoteAwarePlatform::GetHostname() {
   return nullptr;
 }
 
-const char *RemoteAwarePlatform::GetUserName(uint32_t uid) {
-  // Check the cache in Platform in case we have already looked this uid up
-  const char *user_name = Platform::GetUserName(uid);
-  if (user_name)
-    return user_name;
-
-  if (IsRemote() && m_remote_platform_sp)
-    return m_remote_platform_sp->GetUserName(uid);
-  return nullptr;
-}
-
-const char *RemoteAwarePlatform::GetGroupName(uint32_t gid) {
-  const char *group_name = Platform::GetGroupName(gid);
-  if (group_name)
-    return group_name;
-
-  if (IsRemote() && m_remote_platform_sp)
-    return m_remote_platform_sp->GetGroupName(gid);
-  return nullptr;
+UserIDResolver &RemoteAwarePlatform::GetUserIDResolver() {
+  if (IsHost())
+    return HostInfo::GetUserIDResolver();
+  if (m_remote_platform_sp)
+    return m_remote_platform_sp->GetUserIDResolver();
+  return UserIDResolver::GetNoopResolver();
 }
 
 Environment RemoteAwarePlatform::GetEnvironment() {
diff --git a/lldb/source/Utility/CMakeLists.txt b/lldb/source/Utility/CMakeLists.txt
index 03f965465da..34b6fb27e64 100644
--- a/lldb/source/Utility/CMakeLists.txt
+++ b/lldb/source/Utility/CMakeLists.txt
@@ -85,6 +85,7 @@ add_lldb_library(lldbUtility
   TildeExpressionResolver.cpp
   Timer.cpp
   UserID.cpp
+  UserIDResolver.cpp
   UriParser.cpp
   UUID.cpp
   VASprintf.cpp
diff --git a/lldb/source/Utility/UserIDResolver.cpp b/lldb/source/Utility/UserIDResolver.cpp
new file mode 100644
index 00000000000..8aac6f948cd
--- /dev/null
+++ b/lldb/source/Utility/UserIDResolver.cpp
@@ -0,0 +1,44 @@
+//===-- UserIDResolver.cpp --------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Utility/UserIDResolver.h"
+#include "llvm/Support/ManagedStatic.h"
+
+using namespace lldb_private;
+
+UserIDResolver::~UserIDResolver() = default;
+
+llvm::Optional<llvm::StringRef> UserIDResolver::Get(
+    id_t id, Map &cache,
+    llvm::Optional<std::string> (UserIDResolver::*do_get)(id_t)) {
+
+  std::lock_guard<std::mutex> guard(m_mutex);
+  auto iter_bool = cache.try_emplace(id, llvm::None);
+  if (iter_bool.second)
+    iter_bool.first->second = (this->*do_get)(id);
+  if (iter_bool.first->second)
+    return llvm::StringRef(*iter_bool.first->second);
+  return llvm::None;
+}
+
+namespace {
+class NoopResolver : public UserIDResolver {
+protected:
+  llvm::Optional<std::string> DoGetUserName(id_t uid) override {
+    return llvm::None;
+  }
+
+  llvm::Optional<std::string> DoGetGroupName(id_t gid) override {
+    return llvm::None;
+  }
+};
+} // namespace
+
+static llvm::ManagedStatic<NoopResolver> g_noop_resolver;
+
+UserIDResolver &UserIDResolver::GetNoopResolver() { return *g_noop_resolver; }