Major update to provide thread-safe, robust connection pooling.

Taking inspiration from the waterpark library, the connection pooling
mechanism has been refactored to be thread-safe. Additionally, the
pooling logic detects and handles stale connections in the pool. When a
connection is requested from the pool, the pool first validates that it
is healthy and replaces it with a fresh connection if necessary. This is
transparent to the requester.

Additionally we refactored the internal logging implementation to make
it more conventient to access logging infrastructure and log from
various sub-scopes within fiber_orm (query, pool, etc.)

fiber_orm.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "3.2.0"
+version       = "4.0.0"
 author        = "Jonathan Bernard"
 description   = "Lightweight Postgres ORM for Nim."
 license       = "GPL-3.0"

src/fiber_orm.nim

@@ -286,15 +286,16 @@
 ##
 import std/[json, macros, options, sequtils, strutils]
 import db_connector/db_common
-import namespaced_logging, uuids
+import uuids
 
 from std/unicode import capitalize
 
 import ./fiber_orm/db_common as fiber_db_common
-import ./fiber_orm/pool
-import ./fiber_orm/util
+import ./fiber_orm/[pool, util]
+import ./fiber_orm/private/logging
 
 export pool, util
+export logging.enableDbLogging
 
 type
   PagedRecords*[T] = object
@@ -308,26 +309,6 @@ type
   NotFoundError* = object of CatchableError
     ## Error type raised when no record matches a given ID
 
-var logService {.threadvar.}: Option[ThreadLocalLogService]
-var logger {.threadvar.}: Option[Logger]
-
-proc makeQueryLogEntry(
-    m: string,
-    sql: string,
-    args: openArray[(string, string)] = []): JsonNode =
-  result = %*{ "method": m, "sql": sql }
-  for (k, v) in args: result[k] = %v
-
-proc logQuery*(methodName: string, sqlStmt: string, args: openArray[(string, string)] = []) =
-  # namespaced_logging would do this check for us, but we don't want to even
-  # build the log object if we're not actually logging
-  if logService.isNone: return
-  if logger.isNone: logger = logService.getLogger("fiber_orm/query")
-  logger.debug(makeQueryLogEntry(methodName, sqlStmt, args))
-
-proc enableDbLogging*(svc: ThreadLocalLogService) =
-  logService = some(svc)
-
 proc newMutateClauses(): MutateClauses =
   return MutateClauses(
     columns: @[],
@@ -353,7 +334,7 @@ proc createRecord*[D: DbConnType, T](db: D, rec: T): T =
     " RETURNING " & columnNamesForModel(rec).join(",")
 
   logQuery("createRecord", sqlStmt)
-  debug(logService.getLogger("fiber_orm/query"), %*{ "values": mc.values })
+  debug(getLogger("query"), %*{ "values": mc.values })
 
   let newRow = db.getRow(sql(sqlStmt), mc.values)
 
@@ -845,35 +826,6 @@ macro generateJoinTableProcs*(
       db.withConnection conn:
         associate(conn, `joinTableNameNode`, rec1, rec2)
 
-proc initPool*[D: DbConnType](
-    connect: proc(): D,
-    poolSize = 10,
-    hardCap = false,
-    healthCheckQuery = "SELECT 'true' AS alive"): DbConnPool[D] =
-
-  ## Initialize a new DbConnPool. See the `initDb` procedure in the `Example
-  ## Fiber ORM Usage`_ for an example
-  ##
-  ## * `connect` must be a factory which creates a new `DbConn`.
-  ## * `poolSize` sets the desired capacity of the connection pool.
-  ## * `hardCap` defaults to `false`.
-  ##   When `false`, the pool can grow beyond the configured capacity, but will
-  ##   release connections down to the its capacity (no less than `poolSize`).
-  ##
-  ##   When `true` the pool will not create more than its configured capacity.
-  ##   It a connection is requested, none are free, and the pool is at
-  ##   capacity, this will result in an Error being raised.
-  ## * `healthCheckQuery` should be a simple and fast SQL query that the pool
-  ##   can use to test the liveliness of pooled connections.
-  ##
-  ## .. _Example Fiber ORM Usage: #basic-usage-example-fiber-orm-usage
-
-  initDbConnPool(DbConnPoolConfig[D](
-    connect: connect,
-    poolSize: poolSize,
-    hardCap: hardCap,
-    healthCheckQuery: healthCheckQuery))
-
 template inTransaction*(db, body: untyped) =
   db.withConnection conn:
     conn.exec(sql"BEGIN TRANSACTION")

src/fiber_orm/pool.nim

@@ -4,85 +4,77 @@
 
 ## Simple database connection pooling implementation compatible with Fiber ORM.
 
-import std/[sequtils, sugar]
+when (NimMajor, NimMinor, NimPatch) < (2, 0, 0):
+  when not defined(gcArc) and not defined (gcOrc):
+    {.error: "fiber_orm requires either --mm:arc or --mm:orc.".}
+
+import std/[deques, locks, sequtils, sugar]
 import db_connector/db_common
 
 from db_connector/db_sqlite import getRow, close
 from db_connector/db_postgres import getRow, close
 
 import ./db_common as fiber_db_common
+import ./private/logging
 
 type
-  DbConnPoolConfig*[D: DbConnType] = object
-    connect*: () -> D   ## Factory procedure to create a new DBConn
-    poolSize*: int      ## The pool capacity.
+  DbConnPool*[D: DbConnType] = ptr DbConnPoolObj[D]
 
-    hardCap*: bool      ## Is the pool capacity a hard cap?
-                        ##
-                        ## When `false`, the pool can grow beyond the
-                        ## configured capacity, but will release connections
-                        ## down to the its capacity (no less than `poolSize`).
-                        ##
-                        ## When `true` the pool will not create more than its
-                        ## configured capacity.  It a connection is requested,
-                        ## none are free, and the pool is at capacity, this
-                        ## will result in an Error being raised.
-
-    healthCheckQuery*: string ## Should be a simple and fast SQL query that the
-                              ## pool can use to test the liveliness of pooled
-                              ## connections.
-
-  PooledDbConn[D: DbConnType] = ref object
-    conn: D
-    id: int
-    free: bool
-
-  DbConnPool*[D: DbConnType] = ref object
+  DbConnPoolObj[D: DbConnType] = object
     ## Database connection pool
-    conns: seq[PooledDbConn[D]]
-    cfg: DbConnPoolConfig[D]
-    lastId: int
+    connect: proc (): D {.raises: [DbError].}
+    healthCheckQuery: SqlQuery
+    entries: Deque[D]
+    cond: Cond
+    lock: Lock
 
-proc initDbConnPool*[D: DbConnType](cfg: DbConnPoolConfig[D]): DbConnPool[D] =
-  result = DbConnPool[D](
-    conns: @[],
-    cfg: cfg)
 
-proc newConn[D: DbConnType](pool: DbConnPool[D]): PooledDbConn[D] =
-  pool.lastId += 1
-  {.gcsafe.}:
-    let conn = pool.cfg.connect()
-    result = PooledDbConn[D](
-      conn: conn,
-      id: pool.lastId,
-      free: true)
-    pool.conns.add(result)
+proc close*[D: DbConnType](pool: DbConnPool[D]) =
+  ## Safely close all connections and release resources for the given pool.
+  getLogger("pool").debug("closing connection pool")
+  withLock(pool.lock):
+    while pool.entries.len > 0: close(pool.entries.popFirst())
 
-proc maintain[D: DbConnType](pool: DbConnPool[D]): void =
-  pool.conns.keepIf(proc (pc: PooledDbConn[D]): bool =
-    if not pc.free: return true
+  deinitLock(pool.lock)
+  deinitCond(pool.cond)
+  `=destroy`(pool[])
+  deallocShared(pool)
 
-    try:
-      discard getRow(pc.conn, sql(pool.cfg.healthCheckQuery), [])
-      return true
-    except:
-      try: pc.conn.close()  # try to close the connection
-      except: discard ""
-      return false
-  )
 
-  let freeConns = pool.conns.filterIt(it.free)
-  if pool.conns.len > pool.cfg.poolSize and freeConns.len > 0:
-    let numToCull = min(freeConns.len, pool.conns.len - pool.cfg.poolSize)
+proc newDbConnPool*[D: DbConnType](
+    poolSize: int,
+    connectFunc: proc(): D {.raises: [DbError].},
+    healthCheckQuery = "SELECT 1;"): DbConnPool[D] =
+  ## Initialize a new DbConnPool. See the `initDb` procedure in the `Example
+  ## Fiber ORM Usage`_ for an example
+  ##
+  ## * `connect` must be a factory which creates a new `DbConn`.
+  ## * `poolSize` sets the desired capacity of the connection pool.
+  ## * `healthCheckQuery` should be a simple and fast SQL query that the pool
+  ##   can use to test the liveliness of pooled connections. By default it uses
+  ##   `SELECT 1;`
+  ##
+  ## .. _Example Fiber ORM Usage: ../fiber_orm.html#basic-usage-example-fiber-orm-usage
 
-    if numToCull > 0:
-      let toCull = freeConns[0..numToCull]
-      pool.conns.keepIf((pc) => toCull.allIt(it.id != pc.id))
-      for culled in toCull:
-        try: culled.conn.close()
-        except: discard ""
+  result = cast[DbConnPool[D]](allocShared0(sizeof(DbConnPoolObj[D])))
+  initCond(result.cond)
+  initLock(result.lock)
+  result.entries = initDeque[D](poolSize)
+  result.connect = connectFunc
+  result.healthCheckQuery = sql(healthCheckQuery)
 
-proc take*[D: DbConnType](pool: DbConnPool[D]): tuple[id: int, conn: D] =
+  try:
+    for _ in 0 ..< poolSize: result.entries.addLast(connectFunc())
+  except DbError as ex:
+    try: result.close()
+    except: discard
+    getLogger("pool").error(
+      msg = "unable to initialize connection pool",
+      err = ex)
+    raise ex
+
+
+proc take*[D: DbConnType](pool: DbConnPool[D]): D {.raises: [DbError], gcsafe.} =
   ## Request a connection from the pool. Returns a DbConn if the pool has free
   ## connections, or if it has the capacity to create a new connection. If the
   ## pool is configured with a hard capacity limit and is out of free
@@ -90,25 +82,33 @@ proc take*[D: DbConnType](pool: DbConnPool[D]): tuple[id: int, conn: D] =
   ##
   ## Connections taken must be returned via `release` when the caller is
   ## finished using them in order for them to be released back to the pool.
-  pool.maintain
-  let freeConns = pool.conns.filterIt(it.free)
+  withLock(pool.lock):
+    while pool.entries.len == 0: wait(pool.cond, pool.lock)
+    result = pool.entries.popFirst()
 
-  let reserved =
-    if freeConns.len > 0: freeConns[0]
-    else: pool.newConn()
+    # check that the connection is healthy
+    try: discard getRow(result, pool.healthCheckQuery, [])
+    except DbError:
+      {.gcsafe.}:
+        # if it's not, let's try to close it and create a new connection
+        try:
+          getLogger("pool").info(
+            "pooled connection failed health check, opening a new connection")
+          close(result)
+        except: discard
+        result = pool.connect()
 
-  reserved.free = false
-  return (id: reserved.id, conn: reserved.conn)
 
-proc release*[D: DbConnType](pool: DbConnPool[D], connId: int): void =
+proc release*[D: DbConnType](pool: DbConnPool[D], conn: D) {.raises: [], gcsafe.} =
   ## Release a connection back to the pool.
-  let foundConn = pool.conns.filterIt(it.id == connId)
-  if foundConn.len > 0: foundConn[0].free = true
+  withLock(pool.lock):
+    pool.entries.addLast(conn)
+  signal(pool.cond)
 
 template withConnection*[D: DbConnType](pool: DbConnPool[D], conn, stmt: untyped): untyped =
   ## Convenience template to provide a connection from the pool for use in a
   ## statement block, automatically releasing that connnection when done.
   block:
-    let (connId, conn) = take(pool)
+    let conn = take(pool)
     try: stmt
-    finally: release(pool, connId)
+    finally: release(pool, conn)

src/fiber_orm/private/logging.nim

@@ -0,0 +1,34 @@
+import std/[json, options]
+
+import namespaced_logging
+
+export namespaced_logging.log
+export namespaced_logging.debug
+export namespaced_logging.info
+export namespaced_logging.notice
+export namespaced_logging.warn
+export namespaced_logging.error
+export namespaced_logging.fatal
+
+var logService {.threadvar.}: Option[ThreadLocalLogService]
+var logger {.threadvar.}: Option[Logger]
+
+proc makeQueryLogEntry(
+    m: string,
+    sql: string,
+    args: openArray[(string, string)] = []): JsonNode =
+  result = %*{ "method": m, "sql": sql }
+  for (k, v) in args: result[k] = %v
+
+proc logQuery*(methodName: string, sqlStmt: string, args: openArray[(string, string)] = []) =
+  # namespaced_logging would do this check for us, but we don't want to even
+  # build the log object if we're not actually logging
+  if logService.isNone: return
+  if logger.isNone: logger = logService.getLogger("fiber_orm/query")
+  logger.debug(makeQueryLogEntry(methodName, sqlStmt, args))
+
+proc enableDbLogging*(svc: ThreadLocalLogService) =
+  logService = some(svc)
+
+proc getLogger*(scope: string): Option[Logger] =
+  logService.getLogger("fiber_orm/" & scope)