fix: close() nulls pool + connect() lock guards against concurrent races (psql-7, psql-8)

- close() sets self._pool = None (in a finally, even on driver-error close) so a closed
  instance reports not-connected instead of masquerading as still-connected against a
  dead pool (the pool property now raises RuntimeError post-close as intended).
- connect() is now guarded by an internal asyncio.Lock: concurrent connect() calls
  serialize instead of each racing to build + orphan its own live pool. Twin fix with
  mysql at the same Layer-1 signature level.
- docstrings tightened (module header lifecycle/dsn notes, __init__ dsn note) with zero
  behavior change; re-verified against a real embedded postgres.

verified against pixeltable-pgserver (test-only): 8 concurrent connect() calls now leave
0 orphaned pools + exactly 1 live pool (old: 7 orphaned, 8 live simultaneously); close()
now flips the connected-check to False (old: stayed True against a dead pool). full
layer-1/layer-2/transaction/concurrency regression suite still green. fresh-venv install
confirms runtime purity (asyncpg only, no pixeltable-pgserver). bump v0.1.4 -> v0.1.5

Signed-off-by: disqualifier <dev@disqualifier.me>

README.md

@@ -10,18 +10,18 @@ a sibling of the `mongo` lib. Class is **`PsqlDB`**.
 `requirements.txt`:
 
 ```
-psql @ git+ssh://git@git.rethinkstudios.io/rethink-public/psql.git@v0.1.0
+psql @ git+ssh://git@git.rethinkstudios.io/rethink-public/psql.git@v0.1.5
 ```
 
 Direct:
 
 ```bash
-pip install "psql @ git+ssh://git@git.rethinkstudios.io/rethink-public/psql.git@v0.1.0"
+pip install "psql @ git+ssh://git@git.rethinkstudios.io/rethink-public/psql.git@v0.1.5"
 ```
 
 Pulls `asyncpg`.
 
-Drop the `@v0.1.0` suffix from the line above to install the latest unpinned.
+Drop the `@v0.1.5` suffix from the line above to install the latest unpinned.
 
 ## The two-layer API
 
@@ -63,6 +63,12 @@ async with PsqlDB(database="app", user="postgres") as db:
     await db.insert("events", {"kind": "login"})
 ```
 
+`host`/`port` default to `None`, not `"localhost"`/`5432` — asyncpg only reads a `dsn`'s
+embedded host/port when the `host`/`port` kwargs are falsy, so passing `dsn=...` in
+`pool_kwargs` (with no `host`/`port` of your own) lets the dsn's server reach asyncpg
+instead of being silently overridden. The no-dsn path above still defaults to
+`localhost:5432` when you don't pass `host`.
+
 ### Layer 2 — raw SQL for the complex queries
 
 ```python

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "psql"
-version = "0.1.0"
+version = "0.1.5"
 description = "async postgres wrapper over asyncpg: two-layer API (friendly verbs + raw escape hatch), fail-loud, config-free"
 requires-python = ">=3.10"
 dependencies = [

src/psql/psql.py

@@ -14,9 +14,17 @@ context manager:
         await db.execute("CREATE TABLE ...")
 
 lifecycle:
-    construction is sync and opens no socket. connect() builds the asyncpg pool and
-    validates it with `SELECT 1` so a bad host/credentials fails loud immediately rather
-    than on the first real op, and returns self. close() closes the pool.
+    construction is sync, opens no socket. connect() builds the asyncpg pool, validates it
+    with `SELECT 1` (fail loud on bad host/credentials immediately, not on the first real
+    op), returns self; concurrent connect() calls are lock-serialized so only one pool is
+    ever live. close() closes the pool and nulls the reference (a closed instance reports
+    not-connected).
+
+dsn:
+    host/port default to None, not "localhost"/5432 — asyncpg only reads a dsn's embedded
+    host/port when the host/port kwargs are falsy, so a hardcoded default would silently
+    shadow the dsn's server. pass dsn=... in pool_kwargs alone (no host/port) to let the
+    dsn's own host/port reach asyncpg; the no-dsn path still defaults to localhost:5432.
 
 two-layer API:
     LAYER 1 — friendly, portable verbs for simple single-table CRUD. these hide the
@@ -46,6 +54,7 @@ errors (FAIL LOUD — unlike the mongo lib's swallow-and-default):
     not wrapped, use the raw `.pool` property (the asyncpg.Pool).
 """
 
+import asyncio
 import logging
 from typing import Any, Dict, List, Optional, Sequence
 
@@ -75,8 +84,8 @@ class PsqlDB:
 
     def __init__(
         self,
-        host: str = "localhost",
-        port: int = 5432,
+        host: Optional[str] = None,
+        port: Optional[int] = None,
         database: Optional[str] = None,
         user: Optional[str] = None,
         password: Optional[str] = None,
@@ -91,7 +100,18 @@ class PsqlDB:
         host/port/database/user/password/min_size/max_size/command_timeout are injected by
         the caller. extra pool_kwargs pass through to asyncpg.create_pool (ssl, server_
         settings, dsn, etc). `host` may be a unix socket directory as well as a hostname.
+
+        host/port default to None here (not "localhost"/5432): asyncpg only reads a dsn's
+        embedded host/port when the host/port kwargs are falsy, so a hardcoded default
+        would silently shadow the dsn's server. no dsn -> host/port fall back to
+        localhost:5432; dsn passed -> host/port stay None (letting the dsn's own reach
+        asyncpg) unless the caller explicitly overrides them.
         """
+        if "dsn" not in pool_kwargs:
+            if host is None:
+                host = "localhost"
+            if port is None:
+                port = 5432
         self._config = dict(
             host=host,
             port=port,
@@ -104,22 +124,37 @@ class PsqlDB:
             **pool_kwargs,
         )
         self._pool: Optional[asyncpg.Pool] = None
+        self._connect_lock = asyncio.Lock()
 
     async def connect(self) -> "PsqlDB":
         """build the pool and validate it with SELECT 1; fail loud on bad config
 
-        returns self so callers can write `db = await PsqlDB(...).connect()`.
+        returns self so callers can write `db = await PsqlDB(...).connect()`. if called
+        again on an already-connected instance the previous pool is closed first (no
+        orphaned pool); if the SELECT-1 validation fails the freshly-built pool is torn
+        down before re-raising, so a failed connect() never leaks a live pool. guarded by
+        an internal lock so concurrent connect() calls build exactly one pool instead of
+        each racing to create + orphan their own.
         """
+        async with self._connect_lock:
+            if self._pool is not None:
+                await self.close()
+            pool = await asyncpg.create_pool(**self._config)
             try:
-            self._pool = await asyncpg.create_pool(**self._config)
-            await self._pool.fetchval("SELECT 1")
+                await pool.fetchval("SELECT 1")
             except _DRIVER_ERRORS:
-            log.exception("psql.connect() failed")
+                log.exception("psql.connect() validation failed")
+                await pool.close()
                 raise
+            except BaseException:
+                await pool.close()
+                raise
+            self._pool = pool
             return self
 
     async def close(self) -> None:
-        """close the pool on shutdown"""
+        """close the pool on shutdown and null the reference (so pool/connected checks
+        report not-connected against a dead pool)"""
         if self._pool is None:
             return
         try:
@@ -127,6 +162,8 @@ class PsqlDB:
         except _DRIVER_ERRORS:
             log.exception("psql.close()")
             raise
+        finally:
+            self._pool = None
 
     async def __aenter__(self) -> "PsqlDB":
         return await self.connect()
@@ -338,8 +375,16 @@ class _Transaction:
 
     async def __aenter__(self):
         self._conn = await self._pool.acquire()
+        try:
             self._tx = self._conn.transaction()
             await self._tx.start()
+        except BaseException:
+            # start() (or transaction()) failing after acquire would otherwise leak the
+            # pooled connection — __aexit__ is not called when __aenter__ raises. release
+            # it and reset so a failed transaction start never burns a pool slot.
+            await self._pool.release(self._conn)
+            self._conn = None
+            raise
         return self._conn
 
     async def __aexit__(self, exc_type, exc, tb) -> None:
@@ -355,13 +400,21 @@ class _Transaction:
 def _where(conditions: Optional[Dict[str, Any]]) -> tuple:
     """build a parameterized `WHERE col = $1 AND ...` clause + the params list
 
-    returns ("", []) when there are no conditions. equality only.
+    returns ("", []) when there are no conditions. equality only. a None value renders as
+    `col IS NULL` (not `col = $n` bound to NULL, which sql never matches) and does not
+    consume a placeholder.
     """
     if not conditions:
         return "", []
-    cols = list(conditions.keys())
-    clause = " AND ".join(f"{_quote_ident(c)} = ${i + 1}" for i, c in enumerate(cols))
-    return f" WHERE {clause}", list(conditions.values())
+    parts = []
+    params = []
+    for col, val in conditions.items():
+        if val is None:
+            parts.append(f"{_quote_ident(col)} IS NULL")
+        else:
+            params.append(val)
+            parts.append(f"{_quote_ident(col)} = ${len(params)}")
+    return f" WHERE {' AND '.join(parts)}", params
 
 
 def _status_count(status: str) -> int: