From 7d7a5d9b46bcc9b4a98f5d56e970d06bf45a4bf4 Mon Sep 17 00:00:00 2001
From: Zachary Turner <zturner@google.com>
Date: Sat, 4 Mar 2017 16:42:25 +0000
Subject: [PATCH] Truncate thread names if they're too long.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296972 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/Threading.h  |  4 ++++
 lib/Support/Unix/Threading.inc    | 30 +++++++++++++++++++++++++++---
 lib/Support/Windows/Threading.inc |  2 ++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/include/llvm/Support/Threading.h b/include/llvm/Support/Threading.h
index 3b7869b9253..9b6a3b4efdf 100644
--- a/include/llvm/Support/Threading.h
+++ b/include/llvm/Support/Threading.h
@@ -137,6 +137,10 @@ void llvm_execute_on_thread(void (*UserFn)(void *), void *UserData,
   /// this.
   uint64_t get_threadid();
 
+  /// \brief Get the maximum length of a thread name on this platform.
+  /// A value of 0 means there is no limit.
+  constexpr uint32_t get_max_thread_name_length();
+
   /// \brief Set the name of the current thread.  Setting a thread's name can
   /// be helpful for enabling useful diagnostics under a debugger or when
   /// logging.  The level of support for setting a thread's name varies
diff --git a/lib/Support/Unix/Threading.inc b/lib/Support/Unix/Threading.inc
index b031ff4c034..833b6bed4e7 100644
--- a/lib/Support/Unix/Threading.inc
+++ b/lib/Support/Unix/Threading.inc
@@ -109,10 +109,35 @@ uint64_t llvm::get_threadid() {
 }
 
 
+constexpr uint32_t llvm::get_max_thread_name_length() {
+#if defined(__NetBSD__)
+	return PTHREAD_MAX_NAMELEN_NP;
+#elif defined(__APPLE__)
+	return 64;
+#elif defined(__linux__)
+#if HAVE_PTHREAD_SETNAME_NP
+	return 16;
+#else
+	return 0;
+#endif
+#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
+  return 16;
+#else
+  return 0;
+#endif
+}
+
 void llvm::set_thread_name(const Twine &Name) {
   // Make sure the input is null terminated.
   SmallString<64> Storage;
   StringRef NameStr = Name.toNullTerminatedStringRef(Storage);
+
+  // Truncate from the beginning, not the end, if the specified name is too
+  // long.  For one, this ensures that the resulting string is still null
+  // terminated, but additionally the end of a long thread name will usually
+  // be more unique than the beginning, since a common pattern is for similar
+  // threads to share a common prefix.
+  NameStr = NameStr.take_back(get_max_thread_name_length());
   (void)NameStr;
 #if defined(__linux__)
 #if (defined(__GLIBC__) && defined(_GNU_SOURCE)) || defined(__ANDROID__)
@@ -170,15 +195,14 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
   free(kp);
   return;
 #elif defined(__NetBSD__)
-  char buf[PTHREAD_MAX_NAMELEN_NP];
+  char buf[get_max_thread_name_length()];
   ::pthread_getname_np(::pthread_self(), buf, PTHREAD_MAX_NAMELEN_NP);
 
   Name.append(buf, buf + strlen(buf));
 #elif defined(__linux__)
 #if (defined(__GLIBC__) && defined(_GNU_SOURCE)) || defined(__ANDROID__)
 #if HAVE_PTHREAD_GETNAME_NP
-  constexpr int MAXNAMELEN = 16;
-  char Buffer[MAXNAMELEN];
+  char Buffer[get_max_thread_name_length()];
   if (0 == ::pthread_getname_np(::pthread_self(), Buffer, MAXNAMELEN))
     Name.append(Buffer, Buffer + strlen(Buffer));
 #endif
diff --git a/lib/Support/Windows/Threading.inc b/lib/Support/Windows/Threading.inc
index 30086544ab2..8f36f79ca43 100644
--- a/lib/Support/Windows/Threading.inc
+++ b/lib/Support/Windows/Threading.inc
@@ -59,6 +59,8 @@ uint64_t llvm::get_threadid() {
   return uint64_t(::GetCurrentThreadId());
 }
 
+constexpr uint32_t llvm::get_max_thread_name_length() { return 0; }
+
 void llvm::set_thread_name(const Twine &Name) {
 #if defined(_MSC_VER)
   // Make sure the input is null terminated.
-- 
2.50.1