From a1c807cd9571f956de656dd1dcb558323f3705aa Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sun, 23 Aug 2026 23:14:20 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20Offload=20CPU-bound=20bcryp?=
 =?UTF-8?q?t=20operations=20to=20threadpool?=
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In FastAPI, running CPU-bound tasks like password hashing/verification
synchronously blocks the entire event loop, destroying concurrency.
This change offloads these operations to `starlette.concurrency.run_in_threadpool`.

Co-authored-by: benpiper <4343814+benpiper@users.noreply.github.com>
---
 .jules/bolt.md  |  4 ++++
 backend/auth.py | 17 ++++++++++++-----
 backend/main.py |  6 +++---
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index e6d39e6..b09726f 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -16,3 +16,7 @@
 ## 2024-06-28 - Optimize array lookups in high-frequency React event handlers
 **Learning:** Even if data is pre-processed/memoized (like cached `parsedTimestamps`), performing an O(N) linear search on that array inside a high-frequency event handler (like `<video onTimeUpdate>`, which fires multiple times per second) can cause UI stuttering for large arrays.
 **Action:** When searching sorted arrays (like ordered video timestamps) in high-frequency event loops, replace linear iteration loops with an O(log N) binary search to minimize main thread blocking and ensure smooth UI execution.
+
+## 2024-05-22 - Offload CPU-bound tasks in FastAPI
+**Learning:** In FastAPI, CPU-bound tasks like `bcrypt.checkpw` and `bcrypt.hashpw` block the event loop when executed synchronously, significantly reducing API concurrency and throughput for other endpoints.
+**Action:** Always offload CPU-bound hashing operations using `starlette.concurrency.run_in_threadpool` and make the wrapper functions `async` to keep the event loop non-blocking.
diff --git a/backend/auth.py b/backend/auth.py
index f958845..33c53e4 100644
--- a/backend/auth.py
+++ b/backend/auth.py
@@ -5,6 +5,7 @@
 from fastapi.security import OAuth2PasswordBearer
 import bcrypt
 import jwt
+from starlette.concurrency import run_in_threadpool
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select, func
 from models import User
@@ -22,11 +23,17 @@
 
 oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login")
 
-def verify_password(plain_password, hashed_password):
-    return bcrypt.checkpw(plain_password.encode('utf-8'), hashed_password.encode('utf-8'))
+async def verify_password(plain_password, hashed_password):
+    return await run_in_threadpool(
+        bcrypt.checkpw,
+        plain_password.encode('utf-8'),
+        hashed_password.encode('utf-8')
+    )
 
-def get_password_hash(password):
-    return bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt()).decode('utf-8')
+async def get_password_hash(password):
+    return await run_in_threadpool(
+        lambda: bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt()).decode('utf-8')
+    )
 
 def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
     import uuid
@@ -65,7 +72,7 @@ async def initialize_admin_from_env(db: AsyncSession):
     if admin_password_hash:
         hashed = admin_password_hash
     elif admin_password:
-        hashed = get_password_hash(admin_password)
+        hashed = await get_password_hash(admin_password)
     else:
         return False
 
diff --git a/backend/main.py b/backend/main.py
index f637f4a..7c30bd5 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -244,7 +244,7 @@ async def register(user: UserCreate, db: AsyncSession = Depends(get_db)):
     user_count = result.scalar()
     
     is_first_user = user_count == 0
-    hashed_password = get_password_hash(user.password)
+    hashed_password = await get_password_hash(user.password)
     db_user = User(
         email=user.email, 
         hashed_password=hashed_password,
@@ -267,7 +267,7 @@ async def register(user: UserCreate, db: AsyncSession = Depends(get_db)):
 @app.post("/api/auth/login")
 async def login(user: UserLogin, db: AsyncSession = Depends(get_db)):
     db_user = await get_user_by_email(db, user.email)
-    if not db_user or not verify_password(user.password, db_user.hashed_password):
+    if not db_user or not await verify_password(user.password, db_user.hashed_password):
         raise HTTPException(status_code=401, detail="Incorrect email or password")
     
     if not db_user.is_approved:
@@ -320,7 +320,7 @@ async def setup_initial_admin(user: UserCreate, db: AsyncSession = Depends(get_d
     if not user.email or not user.password:
         raise HTTPException(status_code=400, detail="Email and password required")
 
-    hashed_password = get_password_hash(user.password)
+    hashed_password = await get_password_hash(user.password)
     admin_user = User(
         email=user.email,
         hashed_password=hashed_password,