pool.rs

//! A simple connection pool

use std::cell::RefCell;
use sync::MutexArc;

use {PostgresNotifications,
     PostgresCancelData,
     PostgresConnection,
     NormalPostgresStatement,
     PostgresTransaction,
     SslMode};
use error::{PostgresConnectError, PostgresError};
use types::ToSql;

struct InnerConnectionPool {
    url: ~str,
    ssl: SslMode,
    pool: ~[PostgresConnection],
}

impl InnerConnectionPool {
    fn new_connection(&mut self) -> Option<PostgresConnectError> {
        match PostgresConnection::try_connect(self.url, &self.ssl) {
            Ok(conn) => {
                self.pool.push(conn);
                None
            }
            Err(err) => Some(err)
        }
    }
}

/// A simple fixed-size Postgres connection pool.
///
/// It can be shared across tasks.
#[deriving(Clone)]
pub struct PostgresConnectionPool {
    priv pool: MutexArc<InnerConnectionPool>
}

impl PostgresConnectionPool {
    /// Attempts to create a new pool with the specified number of connections.
    ///
    /// Returns an error if the specified number of connections cannot be
    /// created.
    pub fn try_new(url: &str, ssl: SslMode, pool_size: uint)
            -> Result<PostgresConnectionPool, PostgresConnectError> {
        let mut pool = InnerConnectionPool {
            url: url.to_owned(),
            ssl: ssl,
            pool: ~[],
        };

        for _ in range(0, pool_size) {
            match pool.new_connection() {
                None => (),
                Some(err) => return Err(err)
            }
        }

        Ok(PostgresConnectionPool {
            pool: MutexArc::new(pool)
        })
    }

    /// A convenience function wrapping `try_new`.
    ///
    /// # Failure
    ///
    /// Fails if the pool cannot be created.
    pub fn new(url: &str, ssl: SslMode, pool_size: uint)
            -> PostgresConnectionPool {
        match PostgresConnectionPool::try_new(url, ssl, pool_size) {
            Ok(pool) => pool,
            Err(err) => fail!("Unable to initialize pool: {}", err.to_str())
        }
    }

    /// Retrieves a connection from the pool.
    ///
    /// If all connections are in use, blocks until one becomes available.
    pub fn get_connection(&self) -> PooledPostgresConnection {
        let conn = self.pool.access_cond(|pool, cvar| {
            while pool.pool.is_empty() {
                cvar.wait();
            }

            pool.pool.pop().unwrap()
        });

        PooledPostgresConnection {
            pool: self.clone(),
            conn: Some(conn)
        }
    }
}

/// A Postgres connection pulled from a connection pool.
///
/// It will be returned to the pool when it falls out of scope, even due to
/// task failure.
pub struct PooledPostgresConnection {
    priv pool: PostgresConnectionPool,
    // TODO remove the Option wrapper when drop takes self by value
    priv conn: Option<PostgresConnection>
}

impl Drop for PooledPostgresConnection {
    fn drop(&mut self) {
        let conn = RefCell::new(self.conn.take());
        self.pool.pool.access(|pool| {
            pool.pool.push(conn.with_mut(|r| r.take_unwrap()));
        })
    }
}

impl PooledPostgresConnection {
    /// Like `PostgresConnection::try_prepare`.
    pub fn try_prepare<'a>(&'a self, query: &str)
            -> Result<NormalPostgresStatement<'a>, PostgresError> {
        self.conn.get_ref().try_prepare(query)
    }

    /// Like `PostgresConnection::prepare`.
    pub fn prepare<'a>(&'a self, query: &str) -> NormalPostgresStatement<'a> {
        self.conn.get_ref().prepare(query)
    }

    /// Like `PostgresConnection::try_execute`.
    pub fn try_execute(&self, query: &str, params: &[&ToSql])
            -> Result<uint, PostgresError> {
        self.conn.get_ref().try_execute(query, params)
    }

    /// Like `PostgresConnection::execute`.
    pub fn execute(&self, query: &str, params: &[&ToSql]) -> uint {
        self.conn.get_ref().execute(query, params)
    }

    /// Like `PostgresConnection::try_transaction`.
    pub fn try_transaction<'a>(&'a self)
            -> Result<PostgresTransaction<'a>, PostgresError> {
        self.conn.get_ref().try_transaction()
    }

    /// Like `PostgresConnection::transaction`.
    pub fn transaction<'a>(&'a self) -> PostgresTransaction<'a> {
        self.conn.get_ref().transaction()
    }

    /// Like `PostgresConnection::notifications`.
    pub fn notifications<'a>(&'a self) -> PostgresNotifications<'a> {
        self.conn.get_ref().notifications()
    }

    /// Like `PostgresConnection::cancel_data`.
    pub fn cancel_data(&self) -> PostgresCancelData {
        self.conn.get_ref().cancel_data()
    }

    /// Like `PostgresConnection::is_desynchronized`.
    pub fn is_desynchronized(&self) -> bool {
        self.conn.get_ref().is_desynchronized()
    }
}