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@v0.1.4
+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@v0.1.4"
+pip install "psql @ git+ssh://git@git.rethinkstudios.io/rethink-public/psql.git@v0.1.5"
 ```
 
 Pulls `asyncpg`.
 
-Drop the `@v0.1.4` 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
 

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "psql"
-version = "0.1.4"
+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

@@ -14,16 +14,17 @@ context manager:
         await db.execute("CREATE TABLE ...")
 
 lifecycle:
-    construction is sync and opens no socket. connect() builds the asyncpg pool and
+    construction is sync, opens no socket. connect() builds the asyncpg pool, validates it
-    validates it with `SELECT 1` so a bad host/credentials fails loud immediately rather
+    with `SELECT 1` (fail loud on bad host/credentials immediately, not on the first real
-    than on the first real op, and returns self. close() closes the pool.
+    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
+    host/port default to None, not "localhost"/5432 — asyncpg only reads a dsn's embedded
-    embedded host/port when the host/port kwargs are falsy, so a hardcoded default would
+    host/port when the host/port kwargs are falsy, so a hardcoded default would silently
-    silently shadow the dsn's server. pass dsn=... in pool_kwargs alone (no host/port) to
+    shadow the dsn's server. pass dsn=... in pool_kwargs alone (no host/port) to let the
-    let the dsn's own host/port reach asyncpg; the no-dsn path still defaults to
+    dsn's own host/port reach asyncpg; the no-dsn path still defaults to localhost:5432.
-    localhost:5432.
 
 two-layer API:
     LAYER 1 — friendly, portable verbs for simple single-table CRUD. these hide the
@@ -53,6 +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
 
@@ -99,12 +101,11 @@ class PsqlDB:
         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) because asyncpg only reads
+        host/port default to None here (not "localhost"/5432): asyncpg only reads a dsn's
-        a dsn's embedded host/port when the host/port kwargs are falsy — a hardcoded
+        embedded host/port when the host/port kwargs are falsy, so a hardcoded default
-        default would silently shadow the dsn's server and connect you to the wrong one.
+        would silently shadow the dsn's server. no dsn -> host/port fall back to
-        when no dsn is passed, host/port fall back to localhost:5432 (the common no-dsn
+        localhost:5432; dsn passed -> host/port stay None (letting the dsn's own reach
-        path is unchanged); when a dsn is passed, host/port stay None unless the caller
+        asyncpg) unless the caller explicitly overrides them.
-        explicitly overrides them, letting the dsn's own host/port reach asyncpg.
         """
         if "dsn" not in pool_kwargs:
             if host is None:
@@ -123,6 +124,7 @@ 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
@@ -130,8 +132,11 @@ class PsqlDB:
         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.
+        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)
@@ -148,7 +153,8 @@ class PsqlDB:
             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:
@@ -156,6 +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()