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% LISP ABORT

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Reference: ANSI Common Lisp npt
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5.1 LISP ABORT

LISP ABORT is a forced termination due to a system error.
The C language exit function is called with the exit code 1 to terminate the process.

If you want to run abort manually, run the following function.

lisp_abort();

The result is as follows.

$ ./a.out


**************
  LISP ABORT
**************
$ echo $?
1
$

When the statement LISP ABORT is printed, as in the runtime example, it means that the process has been forced to terminate.
The exit code is 1.
The message at the end can be added with the following functions.

void lisp_abortf(const char *fmt, ...);
void lisp_abort8(const void *fmt, ...);
void lisp_abort16(const void *fmt, ...);
void lisp_abort32(const void *fmt, ...);

Functions with 8, 16, or 32 in their names are used to create messages with the lisp_string8_ function.
Because it goes through format, Common Lisp must be running.

The function lisp_abortf takes a format of printf as an argument.
Because it does not go through the format, Common Lisp is not required to be running.

However, the printf cannot take a Lisp object as its argument. (If you could, I think it would be about %p.)

5.2 Handler Settings

The lisp_abort can control the behavior of a handler by registering them.
For example, let’s set up the following handlers.

void test_handler(void)
{
	printf("Hello Handler.\n");
}

The function lisp_set_abort_handler is used to register the handler.
For example, consider the following example.

lisp_set_abort_handler(test_handler);
lisp_abort();

The results are shown below.

$ ./a.out
Hello Handler.


**************
  LISP ABORT
**************
$

After the handler was started, a LISP ABORT occurred and the process was forced to terminate.
Even though the handler has been registered, the interruption process will continue and LISP ABORT will be executed.

5.3 Capturing LISP ABORT

The LISP ABORT can be continued without terminating the process by using setjmp.
To capture and continue, use the following instructions

lisp_set_abort_setjmp_handler sets the handler for capture.
Lisp_abort_Begin and Lisp_abort_End are macros to enclose the capturing process.

The following is an example of capturing LISP ABORT.

int main(void)
{
    lisp_set_abort_setjmp_handler();
    Lisp_abort_Begin {
        printf("Start\n");
        lisp_abort();
        printf("End\n");
    }
    Lisp_abort_End;

    printf("Return\n");

    return 0;
}

The results are as follows.

$ ./a.out
Start
Return
$

The Start and Return are shown in the execution result, but the End is not shown.
This is because the lisp_abort function caused the abort and the process jumped to Lisp_abort_End.
With the above method, it’s hard to tell if the process is a normal end, or if it’s a LISP ABORT occurrence.

So, change it as follows

void main_call(void)
{
    printf("Start\n");
    lisp_abort();
    printf("End\n");
}

int main(void)
{
    int finish;

    lisp_set_abort_setjmp_handler();
    finish = 0;
    Lisp_abort_Begin {
        main_call();
        finish = 1;
    }
    Lisp_abort_End;

    if (finish == 0)
        printf("Lisp Abort\n");

    return 0;
}

A variable finish is prepared and it is assumed to be finished successfully if the value is changed at the end of Lisp_abort_Begin.
The results are shown below.

$ ./a.out
Start
Lisp Abort
$

5.4 Use in C++

The handler for LISP ABORT is setjmp in C, but when compiled in C++ it is changed to try/atch.
The reason for the change is that the destructor will not be invoked if it is setjmp.
As an example, let’s try to run the following statement in C++.

class destruct
{
public:
    destruct() { printf("Constructor\n"); };
    ~destruct() { printf("Destructor\n"); };
};

void main_call(void)
{
    destruct x;

    printf("Start\n");
    lisp_abort();
    printf("End\n");
}

int main(void)
{
    int finish;

    lisp_set_abort_setjmp_handler();
    finish = 0;
    Lisp_abort_Begin {
        main_call();
        finish = 1;
    }
    Lisp_abort_End;

    if (finish == 0)
        printf("Lisp Abort\n");

    return 0;
}

An example is shown below.

$ ./a.out
Constructor
Start
Destructor
Lisp Abort
$

In this example, the destructor is invoked because try/catch is used instead of setjmp.
However, if LISP_ABORT_SETJMP is defined at compile time, C++ compilation will also use setjmp.
The following is the result of executing the above example with setjmp.

$ ./a.out
Constructor
Start
Lisp Abort
$

Since the lisp_abort function is executed, the destructor is ignored because it transitions directly to Lisp_abort_End.

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