reduce lock contention on file open

src/fdcache.cpp

@@ -725,15 +725,12 @@ void FdEntity::Close(void)
   }
 }
 
-int FdEntity::Dup(bool no_fd_lock_wait)
+int FdEntity::Dup()
 {
   S3FS_PRN_DBG("[path=%s][fd=%d][refcnt=%d]", path.c_str(), fd, (-1 != fd ? refcnt + 1 : refcnt));
 
   if(-1 != fd){
-    AutoLock auto_lock(&fdent_lock, no_fd_lock_wait);
-    if (!auto_lock.isLockAcquired()) {
-      return -1;
-    }
+    AutoLock auto_lock(&fdent_lock);
     refcnt++;
   }
   return fd;
@@ -756,13 +753,23 @@ int FdEntity::OpenMirrorFile(void)
     return -EIO;
   }
 
+  // create seed generating mirror file name
+  unsigned int seed = static_cast<unsigned int>(time(NULL));
+  int urandom_fd;
+  if(-1 != (urandom_fd = open("/dev/urandom", O_RDONLY))){
+    unsigned int rand_data;
+    if(sizeof(rand_data) == read(urandom_fd, &rand_data, sizeof(rand_data))){
+      seed ^= rand_data;
+    }
+    close(urandom_fd);
+  }
+
   // try to link mirror file
   while(true){
     // make random(temp) file path
     // (do not care for threading, because allowed any value returned.)
     //
     char         szfile[NAME_MAX + 1];
-    unsigned int seed = static_cast<unsigned int>(time(NULL));
     sprintf(szfile, "%x.tmp", rand_r(&seed));
     mirrorpath = bupdir + "/" + szfile;
 
@@ -774,6 +781,7 @@ int FdEntity::OpenMirrorFile(void)
       S3FS_PRN_ERR("could not link mirror file(%s) to cache file(%s) by errno(%d).", mirrorpath.c_str(), cachepath.c_str(), errno);
       return -errno;
     }
+    ++seed;
   }
 
   // open mirror file
@@ -785,21 +793,20 @@ int FdEntity::OpenMirrorFile(void)
   return mirrorfd;
 }
 
-// [NOTE]
-// This method does not lock fdent_lock, because FdManager::fd_manager_lock
-// is locked before calling.
-//
 int FdEntity::Open(headers_t* pmeta, ssize_t size, time_t time, bool no_fd_lock_wait)
 {
   S3FS_PRN_DBG("[path=%s][fd=%d][size=%jd][time=%jd]", path.c_str(), fd, (intmax_t)size, (intmax_t)time);
 
-  if(-1 != fd){
-    // already opened, needs to increment refcnt.
-    if (fd != Dup(no_fd_lock_wait)) {
+  AutoLock auto_lock(&fdent_lock, no_fd_lock_wait);
+  if (!auto_lock.isLockAcquired()) {
     // had to wait for fd lock, return
     return -EIO;
   }
 
+  if(-1 != fd){
+    // already opened, needs to increment refcnt.
+    Dup();
+
     // check only file size(do not need to save cfs and time.
     if(0 <= size && pagelist.Size() != static_cast<size_t>(size)){
       // truncate temporary file size
@@ -2027,6 +2034,8 @@ FdEntity* FdManager::Open(const char* path, headers_t* pmeta, ssize_t size, time
   if(!path || '\0' == path[0]){
     return NULL;
   }
+  FdEntity* ent;
+  {
     AutoLock auto_lock(&FdManager::fd_manager_lock);
 
     // search in mapping by key(path)
@@ -2045,7 +2054,6 @@ FdEntity* FdManager::Open(const char* path, headers_t* pmeta, ssize_t size, time
       }
     }
 
-  FdEntity* ent;
     if(fent.end() != iter){
       // found
       ent = (*iter).second;
@@ -2078,6 +2086,7 @@ FdEntity* FdManager::Open(const char* path, headers_t* pmeta, ssize_t size, time
     }else{
       return NULL;
     }
+  }
 
   // open
   if(0 != ent->Open(pmeta, size, time, no_fd_lock_wait)){

src/fdcache.h

@@ -146,7 +146,7 @@ class FdEntity
     bool IsOpen(void) const { return (-1 != fd); }
     int Open(headers_t* pmeta = NULL, ssize_t size = -1, time_t time = -1, bool no_fd_lock_wait = false);
     bool OpenAndLoadAll(headers_t* pmeta = NULL, size_t* size = NULL, bool force_load = false);
-    int Dup(bool no_fd_lock_wait = false);
+    int Dup();
 
     const char* GetPath(void) const { return path.c_str(); }
     void SetPath(const std::string &newpath) { path = newpath; }