From 4fd0d45e540902eeecd69670677b023ce9b59a6b Mon Sep 17 00:00:00 2001
From: Jude Nelson <judecn@gmail.com>
Date: Mon, 29 Jan 2018 19:04:59 -0500
Subject: [PATCH] add queue implementation

---
 blockstack/lib/queue.py | 219 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 219 insertions(+)
 create mode 100644 blockstack/lib/queue.py

diff --git a/blockstack/lib/queue.py b/blockstack/lib/queue.py
new file mode 100644
index 000000000..d1ae1007b
--- /dev/null
+++ b/blockstack/lib/queue.py
@@ -0,0 +1,219 @@
+# -*- coding: utf-8 -*-
+"""
+    Blockstack
+    ~~~~~
+    copyright: (c) 2014-2015 by Halfmoon Labs, Inc.
+    copyright: (c) 2016-2018 by Blockstack.org
+
+    This file is part of Blockstack.
+
+    Blockstack is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Blockstack is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+    You should have received a copy of the GNU General Public License
+    along with Blockstack. If not, see <http://www.gnu.org/licenses/>.
+"""
+
+import sqlite3
+import traceback
+import os
+import json
+import base64
+import time
+import random
+import threading
+
+from util import db_query_execute
+
+QUEUE_SQL = """
+CREATE TABLE IF NOT EXISTS queue( name STRING NOT NULL,
+                                  queue_id STRING NOT NULL,
+                                  data NOT NULL );
+"""
+
+from virtualchain import get_logger
+
+log = get_logger()
+
+DB_SERIALIZE_LOCK = threading.Lock()
+
+def queuedb_create(path):
+    """
+    Create a sqlite3 db at the given path.
+    Create all the tables and indexes we need.
+    Raises if the table already exists
+    """
+    
+    global QUEUE_SQL, ERROR_SQL
+
+    lines = [l + ";" for l in QUEUE_SQL.split(";")]
+    con = sqlite3.connect( path, isolation_level=None )
+
+    for line in lines:
+        con.execute(line)
+
+    con.commit()
+    con.row_factory = queuedb_row_factory
+    return con
+
+
+def queuedb_open(path):
+    """
+    Open a connection to the given database.
+    hack: At most one queue-open can happen globally.
+    """
+    with DB_SERIALIZE_LOCK:
+        return queuedb_create( path )
+
+
+def queuedb_row_factory(cursor, row):
+    """
+    Dict row factory
+    """
+    d = {}
+    for idx, col in enumerate(cursor.description):
+        d[col[0]] = row[idx]
+
+    return d
+
+
+def queuedb_query_execute(cur, query, values):
+    """
+    Execute a query.  If it fails, abort the program.
+    Gracefully handle lock contention by timing out.
+    """
+    return db_query_execute(cur, query, values)
+
+
+def queuedb_find(path, queue_id, name, offset=None, limit=None):
+    """
+    Find a record by name and queue ID.
+    Return the rows on success (empty list if not found)
+    Raise on error
+    """
+    return queuedb_findall(path, queue_id, name=name, offset=offset, limit=limit)
+
+
+def queuedb_findall(path, queue_id, name=None, offset=None, limit=None):
+    """
+    Get all queued entries for a queue and a name.
+    If name is None, then find all queue entries
+
+    Return the rows on success (empty list if not found)
+    Raise on error
+    """
+    sql = "SELECT * FROM queue WHERE queue_id = ? ORDER BY rowid ASC"
+    args = (queue_id,)
+    
+    if name:
+        sql += ' AND name = ?'
+        args += (name,)
+
+    if limit:
+        sql += ' LIMIT ?'
+        args += (limit,)
+    
+    if offset:
+        sql += ' OFFSET ?'
+        args += (offset,)
+
+    sql += ';'
+    
+    db = queuedb_open(path)
+    if db is None:
+        raise Exception("Failed to open %s" % path)
+
+    cur = db.cursor()
+    rows = queuedb_query_execute(cur, sql, args)
+
+    count = 0
+    ret = []
+    for row in rows:
+        dat = {}
+        dat.update(row)
+        ret.append(dat)
+
+    db.close()
+    return ret
+
+
+def queuedb_append(path, queue_id, name, data):
+    """
+    Append an element to the back of the queue.
+    Return True on success
+    Raise on error
+    """
+    sql = "INSERT INTO queue VALUES (?,?,?);"
+    args = (name, queue_id, data)
+
+    db = queuedb_open(path)
+    if db is None:
+        raise Exception("Failed to open %s" % path)
+
+    cur = db.cursor()
+    res = queuedb_query_execute(cur, sql, args)
+
+    db.commit()
+    db.close()
+    return True
+
+
+def queuedb_remove(path, entry, cur=None):
+    """
+    Remove an element from a queue.
+    Return True on success
+    Raise on error
+    """
+    sql = "DELETE FROM queue WHERE queue_id = ? AND name = ?;"
+    args = (entry['queue_id'], entry['name'])
+
+    cursor = None
+    if cur:
+        cursor = cur
+    else:
+        db = queuedb_open(path)
+        if db is None:
+            raise Exception("Failed to open %s" % path)
+
+        cursor = db.cursor()
+
+    res = queuedb_query_execute(cursor, sql, args)
+
+    if cur is None:
+        db.commit()
+        db.close()
+
+    return True
+
+
+def queuedb_removeall(path, entries):
+    """
+    Remove all entries from a queue
+    """
+    db = queuedb_open(path)
+    if db is None:
+        raise Exception("Failed to open %s" % path)
+
+    cursor = db.cursor()
+    queuedb_query_execute(cursor, 'BEGIN', ())
+
+    for entry in entries:
+        queuedb_remove(path, entry, cur=cursor)
+
+    queuedb_query_execute(cursor, 'END', ())
+    db.close()
+
+    return True
+
+
+def queuedb_peek(path, queue_id, name):
+    """
+    Find the oldest instance of a named record in a queue.
+    """
+    return queuedb_find( queue_id, name, limit=1, path=path )