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C/C++ API Documentation | 2026.1

# Signaler - interrupt handling

The `Signaler` class enables the API programmer to register functions to be called when the client application receives an interrupt signal. The `Signaler` class maintains a list of registered functions and calls each one in turn. See Signaler methods.

By default, after all of the registered functions have been executed, the process exits, returning `-1` to the operating system.

If using the P4API in an application which is NOT a console app, you must change the default memory management and `exit()` behavior during the initialization of the class.

By default, when the P4API is initialized, it creates the `Signal()` object and provides a default handler. The signaler tracks memory allocations made by `FileSys()` objects and frees those memory allocations on termination. This code is intended for console applications to free allocated memory when an interrupt is processed before `exit()`.

However, if the P4API is used in an environment where the application uses its own memory manager, a crash might occur on exit because the signal handler is trying to free memory from the wrong pool.

To avoid this problem, disable `Signaler()` after the initialization of `P4Libraries`:

    void initializeP4API()
    {
        Error e;
        P4Libraries::Initialize(P4LIBRARIES_INIT_ALL, &e);
        signal(SIGINT, SIG_DFL); // unset the default set by global signaler in C++ so it does not exit
        signaler.Disable(); // disable the global signaler memory tracking at runtime
    }

Otherwise a crash might occur with a call stack similar to this:

    #0 Signaler::DeleteOnIntr (this=0x990330 <signaler>, ptr=0x1ba87e0) at ../p4/sys/signaler.cc:228
    #1 0x00000000004b86e3 in Rpc::~Rpc (this=0x1ba87e0, __in_chrg=<optimized out>) at ../p4/rpc/rpc.cc:312
    #2 0x00000000004d72b7 in Client::~Client (this=0x1ba87e0, __in_chrg=<optimized out>) at ../p4/support/strbuf.h:369
    #3 0x00000000004a7f1c in ClientApi::~ClientApi (this=0x1b9dac0, __in_chrg=<optimized out>) at ../p4/client/clientapi.cc:21

See P4Libraries methods.

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