[RocksDB] Enhance Env to support two thread pools LOW and HIGH

Summary:
this is the ground work for separating memtable flush jobs to their own thread pool.
Both SetBackgroundThreads and Schedule take a third parameter Priority to indicate which thread pool they are working on. The names LOW and HIGH are just identifiers for two different thread pools, and does not indicate real difference in 'priority'. We can set number of threads in the pools independently.
The thread pool implementation is refactored.

Test Plan: make check

Reviewers: dhruba, emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12885

1 files changed, 8 insertions, 6 deletions

diff --git a/hdfs/env_hdfs.h b/hdfs/env_hdfs.h
index bc286fe8d..b9309b3a1 100644
--- a/hdfs/env_hdfs.h
+++ b/hdfs/env_hdfs.h
@@ -107,8 +107,9 @@ class HdfsEnv : public Env {
 
   virtual Status NewLogger(const std::string& fname, Logger** result);
 
-  virtual void Schedule( void (*function)(void* arg), void* arg) {
-    posixEnv->Schedule(function, arg);
+  virtual void Schedule(void (*function)(void* arg), void* arg,
+                        Priority pri = LOW) {
+    posixEnv->Schedule(function, arg, pri);
   }
 
   virtual void StartThread(void (*function)(void* arg), void* arg) {
@@ -140,8 +141,8 @@ class HdfsEnv : public Env {
     return posixEnv->GetAbsolutePath(db_path, output_path);
   }
 
-  virtual void SetBackgroundThreads(int number) {
-    posixEnv->SetBackgroundThreads(number);
+  virtual void SetBackgroundThreads(int number, Priority pri = LOW) {
+    posixEnv->SetBackgroundThreads(number, pri);
   }
 
   virtual std::string TimeToString(uint64_t number) {
@@ -279,7 +280,8 @@ class HdfsEnv : public Env {
   virtual Status NewLogger(const std::string& fname,
                            shared_ptr<Logger>* result){return notsup;}
 
-  virtual void Schedule( void (*function)(void* arg), void* arg) {}
+  virtual void Schedule(void (*function)(void* arg), void* arg,
+                        Priority pri = LOW) {}
 
   virtual void StartThread(void (*function)(void* arg), void* arg) {}
 
@@ -296,7 +298,7 @@ class HdfsEnv : public Env {
   virtual Status GetAbsolutePath(const std::string& db_path,
       std::string* outputpath) {return notsup;}
 
-  virtual void SetBackgroundThreads(int number) {}
+  virtual void SetBackgroundThreads(int number, Priority pri = LOW) {}
 
   virtual std::string TimeToString(uint64_t number) { return "";}
 };