include thread-pool priority in thread names

Summary:
Previously threads were named "rocksdb:bg\<index in thread pool\>", so the first thread in all thread pools would be named "rocksdb:bg0". Users want to be able to distinguish threads used for flush (high-pri) vs regular compaction (low-pri) vs compaction to bottom-level (bottom-pri). So I changed the thread naming convention to include the thread-pool priority.
Closes https://github.com/facebook/rocksdb/pull/3702

Differential Revision: D7581415

Pulled By: ajkr

fbshipit-source-id: ce04482b6acd956a401ef22dc168b84f76f7d7c1

HISTORY.md

@@ -2,6 +2,7 @@
 ## Unreleased
 ### Public API Change
 * Add a BlockBasedTableOption to align uncompressed data blocks on the smaller of block size or page size boundary, to reduce flash reads by avoiding reads spanning 4K pages.
+* The background thread naming convention changed (on supporting platforms) to "rocksdb:<thread pool priority><thread number>", e.g., "rocksdb:low0".
 
 ### New Features
 * Introduce TTL for level compaction so that all files older than ttl go through the compaction process to get rid of old data.

env/env.cc

@@ -22,6 +22,20 @@ namespace rocksdb {
 Env::~Env() {
 }
 
+std::string Env::PriorityToString(Env::Priority priority) {
+  switch (priority) {
+    case Env::Priority::BOTTOM:
+      return "Bottom";
+    case Env::Priority::LOW:
+      return "Low";
+    case Env::Priority::HIGH:
+      return "High";
+    case Env::Priority::TOTAL:
+      assert(false);
+  }
+  return "Invalid";
+}
+
 uint64_t Env::GetThreadID() const {
   std::hash<std::thread::id> hasher;
   return hasher(std::this_thread::get_id());

include/rocksdb/env.h

@@ -302,6 +302,8 @@ class Env {
   // Priority for scheduling job in thread pool
   enum Priority { BOTTOM, LOW, HIGH, TOTAL };
 
+  static std::string PriorityToString(Priority priority);
+
   // Priority for requesting bytes in rate limiter scheduler
   enum IOPriority {
     IO_LOW = 0,

util/threadpool_imp.cc

@@ -20,11 +20,12 @@
 #  include <sys/syscall.h>
 #endif
 
+#include <stdlib.h>
 #include <algorithm>
 #include <atomic>
 #include <condition_variable>
 #include <mutex>
-#include <stdlib.h>
+#include <sstream>
 #include <thread>
 #include <vector>
 
@@ -313,11 +314,14 @@ void ThreadPoolImpl::Impl::StartBGThreads() {
 #if defined(_GNU_SOURCE) && defined(__GLIBC_PREREQ)
 #if __GLIBC_PREREQ(2, 12)
     auto th_handle = p_t.native_handle();
-    char name_buf[16];
+    std::string thread_priority = Env::PriorityToString(GetThreadPriority());
-    snprintf(name_buf, sizeof name_buf, "rocksdb:bg%" ROCKSDB_PRIszt,
+    std::ostringstream thread_name_stream;
-             bgthreads_.size());
+    thread_name_stream << "rocksdb:";
-    name_buf[sizeof name_buf - 1] = '\0';
+    for (char c : thread_priority) {
-    pthread_setname_np(th_handle, name_buf);
+      thread_name_stream << static_cast<char>(tolower(c));
+    }
+    thread_name_stream << bgthreads_.size();
+    pthread_setname_np(th_handle, thread_name_stream.str().c_str());
 #endif
 #endif
     bgthreads_.push_back(std::move(p_t));