PostgreSQL 8.3.1 Documentation
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# 30.17. Behavior in Threaded Programs

libpq is reentrant and thread-safe if the `configure` command-line option `--enable-thread-safety` was used when the PostgreSQL distribution was built. In addition, you might need to use additional compiler command-line options when you compile your application code. Refer to your system's documentation for information about how to build thread-enabled applications, or look in `src/Makefile.global` for `PTHREAD_CFLAGS` and `PTHREAD_LIBS`. This function allows the querying of libpq's thread-safe status:

`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.

One thread 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 read-only after creation, and so can be passed around freely between threads.

The deprecated functions `PQrequestCancel` and `PQoidStatus` are not thread-safe and should not be used in multithread programs. `PQrequestCancel` can be replaced by `PQcancel`. `PQoidStatus` can be replaced by `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.

If you experience problems with threaded applications, run the program in `src/tools/thread` to see if your platform has thread-unsafe functions. This program is run by `configure`, but for binary distributions your library might not match the library used to build the binaries.

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