> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/client-interfaces/libpq/libpq-threading.md).

# 32.21. Behavior in Threaded Programs \#

As of version 17, libpq is always reentrant and thread-safe. However, one restriction is that no two threads attempt to manipulate the same `PGconn` object at the same time. In particular, you cannot issue concurrent commands from different threads through the same connection object. (If you need to run concurrent commands, use multiple connections.)

`PGresult` objects are normally read-only after creation, and so can be passed around freely between threads. However, if you use any of the `PGresult`-modifying functions described in [Section 32.12](/client-interfaces/libpq/libpq-misc.md) or [Section 32.14](/client-interfaces/libpq/libpq-events.md), it's up to you to avoid concurrent operations on the same `PGresult`, too.

In earlier versions, libpq could be compiled with or without thread support, depending on compiler options. This function allows the querying of libpq's thread-safe status:

`PQisthreadsafe` [#](#LIBPQ-PQISTHREADSAFE) : Returns the thread safety status of the libpq library.

````
```

int PQisthreadsafe();
```

Returns 1 if the libpq is thread-safe
and 0 if it is not. Always returns 1 on version 17 and above.
````

The deprecated functions [`PQrequestCancel`](/client-interfaces/libpq/libpq-cancel.md#LIBPQ-PQREQUESTCANCEL) and [`PQoidStatus`](/client-interfaces/libpq/libpq-exec.md#LIBPQ-PQOIDSTATUS) are not thread-safe and should not be used in multithread programs. [`PQrequestCancel`](/client-interfaces/libpq/libpq-cancel.md#LIBPQ-PQREQUESTCANCEL) can be replaced by [`PQcancelBlocking`](/client-interfaces/libpq/libpq-cancel.md#LIBPQ-PQCANCELBLOCKING). [`PQoidStatus`](/client-interfaces/libpq/libpq-exec.md#LIBPQ-PQOIDSTATUS) can be replaced by [`PQoidValue`](/client-interfaces/libpq/libpq-exec.md#LIBPQ-PQOIDVALUE).

If you are using Kerberos inside your application (in addition to inside libpq), you will need to do locking around Kerberos calls because Kerberos functions are not thread-safe. See function `PQregisterThreadLock` in the libpq source code for a way to do cooperative locking between libpq and your application.

Similarly, if you are using Curl inside your application, *and* you do not already [initialize libcurl globally](https://curl.se/libcurl/c/curl_global_init.html) before starting new threads, you will need to cooperatively lock (again via `PQregisterThreadLock`) around any code that may initialize libcurl. This restriction is lifted for more recent versions of Curl that are built to support thread-safe initialization; those builds can be identified by the advertisement of a `threadsafe` feature in their version metadata.

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/libpq-threading.html)（英文原文，待翻譯）


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