Performance drop with using coverage testing starlette websocket

[Randomneo]

Describe the bug
Performance drop with using coverage testing starlette websocket.

To Reproduce
How can we reproduce the problem? Please be specific. Don't link to a failing CI job. Answer the questions below:

1. platform linux -- Python 3.10.5, pytest-7.1.2, pluggy-1.0.0
2. Package versions

>>> coverage.__version__
'6.4.1'
>>> fastapi.__version__
'0.78.0'
>>> starlette.__version__
'0.19.1'

1. code: https://pastebin.com/F2iXUM4E.
2. just running this code with pytest will in average less than 1s. But with pytest --cov or coverage run -m pytest increases its execution time 10 times (10s+ avg)

Expected behavior
Coverage do not affect execution time.

Additional context
As far as I can see problem with async to sync in starlette.testclient.TestClient and coverage.
Also coverage do not affect execution time with concurrency=greenlet (because it wont check any code that way) but execution time raises even more with concurrency=thread.greenlet

[nedbat]

I don't see the same results you do. I had to add a line to your file: from starlette.testclient import TestClient

Then:

% pytest bug1411.py
====================================================================== test session starts =======================================================================
platform darwin -- Python 3.10.5, pytest-7.1.2, pluggy-1.0.0
rootdir: /private/tmp
plugins: anyio-3.6.1, cov-3.0.0
collected 1 item

bug1411.py .                                                                                                                                               [100%]

======================================================================= 1 passed in 0.23s ========================================================================

% coverage run -m pytest bug1411.py
====================================================================== test session starts =======================================================================
platform darwin -- Python 3.10.5, pytest-7.1.2, pluggy-1.0.0
rootdir: /private/tmp
plugins: anyio-3.6.1, cov-3.0.0
collected 1 item

bug1411.py .                                                                                                                                               [100%]

======================================================================= 1 passed in 0.30s ========================================================================

The times are not the same, but they are similar, and within reason. Can you show the results of coverage debug sys? Are you using the C tracer?

[Randomneo]

% coverage debug sys
-- sys -------------------------------------------------------
               coverage_version: 6.4.1
                coverage_module: /home/randomneo/.virtualenvs/default/lib/python3.10/site-packages/coverage/__init__.py
                         tracer: -none-
                        CTracer: available
           plugins.file_tracers: -none-
            plugins.configurers: -none-
      plugins.context_switchers: -none-
              configs_attempted: .coveragerc
                                 setup.cfg
                                 tox.ini
                                 pyproject.toml
                   configs_read: -none-
                    config_file: None
                config_contents: -none-
                      data_file: -none-
                         python: 3.10.5 (main, Jun  6 2022, 18:49:26) [GCC 12.1.0]
                       platform: Linux-5.18.7-arch1-1-x86_64-with-glibc2.35
                 implementation: CPython
                     executable: /home/randomneo/.virtualenvs/default/bin/python
                   def_encoding: utf-8
                    fs_encoding: utf-8
                            pid: 2569
                            cwd: /home/randomneo/projects/personal/fastapi_websocket_slow
                           path: /home/randomneo/.virtualenvs/default/bin
                                 /usr/lib/python310.zip
                                 /usr/lib/python3.10
                                 /usr/lib/python3.10/lib-dynload
                                 /home/randomneo/.virtualenvs/default/lib/python3.10/site-packages
                    environment: HOME = /home/randomneo
                   command_line: /home/randomneo/.virtualenvs/default/bin/coverage debug sys
                sqlite3_version: 2.6.0
         sqlite3_sqlite_version: 3.38.5
             sqlite3_temp_store: 0
        sqlite3_compile_options: ATOMIC_INTRINSICS=1, COMPILER=gcc-12.1.0, DEFAULT_AUTOVACUUM,
                                 DEFAULT_CACHE_SIZE=-2000, DEFAULT_FILE_FORMAT=4,
                                 DEFAULT_JOURNAL_SIZE_LIMIT=-1, DEFAULT_MMAP_SIZE=0, DEFAULT_PAGE_SIZE=4096,
                                 DEFAULT_PCACHE_INITSZ=20, DEFAULT_RECURSIVE_TRIGGERS,
                                 DEFAULT_SECTOR_SIZE=4096, DEFAULT_SYNCHRONOUS=2,
                                 DEFAULT_WAL_AUTOCHECKPOINT=1000, DEFAULT_WAL_SYNCHRONOUS=2,
                                 DEFAULT_WORKER_THREADS=0, ENABLE_COLUMN_METADATA, ENABLE_DBSTAT_VTAB,
                                 ENABLE_FTS3, ENABLE_FTS3_TOKENIZER, ENABLE_FTS4, ENABLE_FTS5,
                                 ENABLE_MATH_FUNCTIONS, ENABLE_RTREE, ENABLE_STMTVTAB, ENABLE_UNLOCK_NOTIFY,
                                 HAVE_ISNAN, MALLOC_SOFT_LIMIT=1024, MAX_ATTACHED=10, MAX_COLUMN=2000,
                                 MAX_COMPOUND_SELECT=500, MAX_DEFAULT_PAGE_SIZE=8192, MAX_EXPR_DEPTH=10000,
                                 MAX_FUNCTION_ARG=127, MAX_LENGTH=1000000000, MAX_LIKE_PATTERN_LENGTH=50000,
                                 MAX_MMAP_SIZE=0x7fff0000, MAX_PAGE_COUNT=1073741823, MAX_PAGE_SIZE=65536,
                                 MAX_SQL_LENGTH=1000000000, MAX_TRIGGER_DEPTH=1000,
                                 MAX_VARIABLE_NUMBER=250000, MAX_VDBE_OP=250000000, MAX_WORKER_THREADS=8,
                                 MUTEX_PTHREADS, SECURE_DELETE, SYSTEM_MALLOC, TEMP_STORE=1, THREADSAFE=1

➜  fastapi_websocket_slow pytest main.py                          (env: default) 
========================== test session starts =============================
platform linux -- Python 3.10.5, pytest-7.1.2, pluggy-1.0.0
rootdir: /home/randomneo/projects/personal/fastapi_websocket_slow, configfile: pytest.ini
plugins: cov-3.0.0, anyio-3.6.1
collected 1 item         

main.py .                                                          [100%]

========================= 1 passed in 1.54s ==========================================  =
➜  fastapi_websocket_slow pytest main.py --cov                       (env: default) 
========================= test session starts ===========================================
platform linux -- Python 3.10.5, pytest-7.1.2, pluggy-1.0.0
rootdir: /home/randomneo/projects/personal/fastapi_websocket_slow, configfile: pytest.ini
plugins: cov-3.0.0, anyio-3.6.1
collected 1 item 

main.py .                                                 [100%]

---------- coverage: platform linux, python 3.10.5-final-0 -----------
Name      Stmts   Miss  Cover
-----------------------------
main.py      23      0   100%
-----------------------------
TOTAL        23      0   100%



================================= 1 passed in 22.26s ===================================