reuse read and write options

* fixes segfault in del
* fixes initResource freeing options before they get used
* fixes failing test cases
* avoids reallocating options on every access
* deallocates fields in reverse creation order

rocksdb.nim

@@ -15,13 +15,6 @@ when useCApi:
   import rocksdb/librocksdb
   export librocksdb
 
-  template managedResource(name) =
-    template freeResource(r: `rocksdb name t`) =
-      `rocksdb name destroy`(r)
-
-  managedResource(WriteOptions)
-  managedResource(ReadOptions)
-
   type
     RocksPtr[T] = object
       res: T
@@ -31,17 +24,26 @@ when useCApi:
   when false:
     # XXX: generic types cannot have destructors at the moment:
     # https://github.com/nim-lang/Nim/issues/5366
-    proc `=destroy`*[T](rocksPtr: var RocksPtr[T]) =
-      freeResource rocksPtr.res
+      template managedResource(name) =
+        template freeResource(r: `rocksdb name t`) =
+          `rocksdb name destroy`(r)
 
-  proc toRocksPtr[T](res: T): RocksPtr[T] =
-    result.res = res
+      managedResource(WriteOptions)
+      managedResource(ReadOptions)
+      template initResource(resourceName): auto =
+        var p = toRocksPtr(`rocksdb resourceName create`())
+        # XXX: work-around the destructor issue above:
+        # XXX: work-around disabled - it frees the resource too early - need to
+        #      free resource manually!
+        # defer: freeResource p.res
+        p.res
+
+      proc `=destroy`*[T](rocksPtr: var RocksPtr[T]) =
+        freeResource rocksPtr.res
+
+      proc toRocksPtr[T](res: T): RocksPtr[T] =
+        result.res = res
 
-  template initResource(resourceName): auto =
-    var p = toRocksPtr(`rocksdb resourceName create`())
-    # XXX: work-around the destructor issue above:
-    defer: freeResource p.res
-    p.res
 else:
   {.error: "The C++ API of RocksDB is not supported yet".}
 
@@ -62,6 +64,8 @@ type
     db: rocksdb_t
     backupEngine: rocksdb_backup_engine_t
     options: rocksdb_options_t
+    readOptions: rocksdb_readoptions_t
+    writeOptions: rocksdb_writeoptions_t
 
   RocksDBResult*[T] = object
     case ok*: bool
@@ -100,6 +104,8 @@ proc init*(rocks: var RocksDBInstance,
            cpus = countProcessors(),
            createIfMissing = true): RocksDBResult[void] =
   rocks.options = rocksdb_options_create()
+  rocks.readOptions = rocksdb_readoptions_create()
+  rocks.writeOptions = rocksdb_writeoptions_create()
 
   # Optimize RocksDB. This is the easiest way to get RocksDB to perform well:
   rocksdb_options_increase_parallelism(rocks.options, cpus.int32)
@@ -155,10 +161,9 @@ template getImpl {.dirty.} =
   assert key.len > 0
 
   var
-    options = initResource ReadOptions
     errors: cstring
     len: csize
-    data = rocksdb_get(db.db, options,
+    data = rocksdb_get(db.db, db.readOptions,
                        cast[cstring](unsafeAddr key[0]), key.len,
                        addr len, errors.addr)
   bailOnErrors()
@@ -176,10 +181,9 @@ proc put*(db: RocksDBInstance, key, val: KeyValueType): RocksDBResult[void] =
   assert key.len > 0
 
   var
-    options = initResource WriteOptions
     errors: cstring
 
-  rocksdb_put(db.db, options,
+  rocksdb_put(db.db, db.writeOptions,
               cast[cstring](unsafeAddr key[0]), key.len,
               cast[cstring](if val.len > 0: unsafeAddr val[0] else: nil), val.len,
               errors.addr)
@@ -188,19 +192,12 @@ proc put*(db: RocksDBInstance, key, val: KeyValueType): RocksDBResult[void] =
   returnOk()
 
 proc del*(db: RocksDBInstance, key: KeyValueType): RocksDBResult[void] =
-  when false:
-    # XXX: For yet unknown reasons, the code below fails with SIGSEGV.
-    # Investigate if this the correct usage of `rocksdb_delete`.
-    var options = initResource WriteOptions
-    var errors: cstringArray
-    echo key.len
-    rocksdb_delete(db.db, options,
-                   cast[cstring](unsafeAddr key[0]), key.len,
-                   errors)
-    bailOnErrors()
-    returnOk()
-  else:
-    put(db, key, @[])
+  var errors: cstring
+  rocksdb_delete(db.db, db.writeOptions,
+                  cast[cstring](unsafeAddr key[0]), key.len,
+                  errors.addr)
+  bailOnErrors()
+  returnOk()
 
 proc contains*(db: RocksDBInstance, key: KeyValueType): RocksDBResult[bool] =
   assert key.len > 0
@@ -222,6 +219,14 @@ proc backup*(db: RocksDBInstance): RocksDBResult[void] =
 # https://github.com/nim-lang/Nim/issues/8112
 # proc `=destroy`*(db: var RocksDBInstance) =
 proc close*(db: var RocksDBInstance) =
+  template freeField(name) =
+    if db.`name`.isNil:
+      `rocksdb name destroy`(db.`name`)
+      db.`name` = nil
+  freeField(writeOptions)
+  freeField(readOptions)
+  freeField(options)
+
   if not db.backupEngine.isNil:
     rocksdb_backup_engine_close(db.backupEngine)
     db.backupEngine = nil
@@ -229,8 +234,3 @@ proc close*(db: var RocksDBInstance) =
   if not db.db.isNil:
     rocksdb_close(db.db)
     db.db = nil
-
-  if not db.options.isNil:
-    rocksdb_options_destroy(db.options)
-    db.options = nil
-