<h2>catch_exception_raise</h2>

<strong>Server Interface</strong> - Handles the occurrence of an exception within a thread.

<h3>SYNOPSIS</h3>

<strong>kern_return_t catch_exception_raise</strong>

<strong>(mach_port_t</strong> <var>exception_port</var>,

<strong>mach_port_t</strong> <var>thread</var>,

<strong>mach_port_t</strong> <var>task</var>,

<strong>exception_type_t</strong> <var>exception</var>,

<strong>exception_data_t</strong> <var>code</var>,

<strong>mach_msg_type_number_t</strong> <var>code_count</var><strong>);</strong>

<strong>catch_exception_raise_state</strong>

expanded form:

<strong>kern_return_t catch_exception_raise_state</strong>

<strong>(mach_port_t</strong> <var>exception_port</var>,

<strong>exception_type_t</strong> <var>exception</var>,

<strong>exception_data_t</strong> <var>code</var>,

<strong>mach_msg_type_number_t</strong> <var>code_count</var>,

<strong>int *</strong> <var>flavor</var>,

<strong>thread_state_t</strong> <var>in_state</var>,

<strong>mach_msg_type_number_t</strong> <var>in_state_count</var>,

<strong>thread_state_t</strong> <var>out_state</var>,

<strong>mach_msg_type_number_t *</strong> <var>out_state_count</var><strong>);</strong>

<strong>catch_exception_raise_state_identity</strong>

expanded form:

<strong>kern_return_t catch_exception_raise_state_identity</strong>

<strong>(mach_port_t</strong> <var>exception_port</var>,

<strong>mach_port_t</strong> <var>thread</var>,

<strong>mach_port_t</strong> <var>task</var>,

<strong>exception_type_t</strong> <var>exception</var>,

<strong>exception_data_t</strong> <var>code</var>,

<strong>mach_msg_type_number_t</strong> <var>code_count</var>,

<strong>int *</strong> <var>flavor</var>,

<strong>thread_state_t</strong> <var>in_state</var>,

<strong>mach_msg_type_number_t</strong> <var>in_state_count</var>,

<strong>thread_state_t</strong> <var>out_state</var>,

<strong>mach_msg_type_number_t *</strong> <var>out_state_count</var><strong>);</strong>

<h3>PARAMETERS</h3>

<dt> <var>exception_port</var>

[in exception (receive) right] The port to which the exception

notification was sent.

<dt> <var>thread</var>

[in thread-self send right] The thread self port for the thread taking the

exception.

<dt> <var>task</var>

[in task-self send right] The task self port for the task containing the

thread taking the exception.

<dt> <var>exception</var>

[in scalar] The type of the exception.

The machine independent values raised by all implementations are:

<dl>

<dt> EXC_BAD_ACCESS

Could not access memory. subcode contains the bad memory

address.

<dt> EXC_BAD_INSTRUCTION

Instruction failed. Illegal or undefined instruction or operand.

<dt> EXC_ARITHMETIC

Arithmetic exception; exact nature of exception is in subcode

field.

<dt> EXC_EMULATION

Emulation instruction. Emulation support instruction encountered.

Details in subcode field.

<dt> EXC_SOFTWARE

Software generated exception; exact exception is in subcode

field. Codes 0 - 0xFFFF reserved to hardware; codes 0x10000

- 0x1FFFF reserved for OS emulation.

<dt> EXC_BREAKPOINT

Trace, breakpoint, etc. Details in subcode field.

<dt> EXC_SYSCALL

System call requested. Details in subcode field.

<dt> EXC_MACH_SYSCALL

System call with a number in the Mach call range requested.

Details in subcode field.

</dl

<dt> <var>code</var>

[in scalar] A machine dependent array indicating a particular instance

of exception.

<dt> <var>code_count</var>

[in scalar] The size of the buffer (in natural-sized units).

<dt> <var>flavor</var>

[pointer to in/out scalar] On input, the type of state included as selected

when the exception port was set. On output, the type of state being

returned.

<dt> <var>in_state</var>

[pointer to in structure] State information of the thread at the time of

the exception.

<dt> <var>in_state_count</var>

[in scalar] The size of the in state buffer (in natural-sized units).

<dt> <var>out_state</var>

[out structure] The state the thread will have if continued from the

point of the exception. The maximum size of this array is

THREAD_STATE_MAX.

<dt> <var>out_state_count</var>

[pointer to out scalar] The size of the out state buffer (in natural-sized units).

</dl>

<h3>DESCRIPTION</h3>

A <strong>catch_exception_raise</strong> function is called by

<strong>exc_server</strong> as the result of a

kernel message indicating that an exception occurred within a thread.

The <var>exception_port</var> parameter specifies the port named via

a previous call to <strong>thread_set_exception_ports</strong> or

<strong>task_set_exception_ports</strong>

as the port that responds when the thread takes an

exception.

The alternate message forms (the format being selected when the exception port

was set) allow for selected thread state to be included.

<h3>NOTES</h3>

When an exception occurs in a thread, the thread sends an exception message to

its exception port, blocking in the kernel waiting for the receipt of a reply. It is

assumed that some task is listening

(most likely with <strong>mach_msg_server</strong>) to this

port, using the <strong>exc_server</strong> function

to decode the messages and then call the

linked in <strong>catch_exception_raise</strong>.

It is the job of <strong>catch_exception_raise</strong> to handle

the exception and decide the course of action for thread.

<p>

If the thread should continue from the point of exception,

<strong>catch_exception_raise</strong> would return KERN_SUCCESS. This causes a reply

message to be sent to the kernel, which will allow the thread to continue from

the point of the exception.

If some other action should be taken by thread, the following actions should be

performed by <strong>catch_exception_raise</strong>:

<dl>

<dt> <strong>thread_suspend</strong>

<dd>

This keeps the thread from proceeding after the next step.

<p>

<dt> <strong>thread_abort</strong>

<dd>

This aborts the message receive operation currently blocking

the thread.

<p>

<dt> <strong>thread_set_state</strong>

<dd>

(if using the <strong>catch_exception_raise</strong> form). Set the

thread's state so that it continues doing something else.

<p>

<dt> <strong>thread_resume</strong>

<dd>

Let the thread start running from its new state.

Returning a value other than KERN_SUCCESS insures that no reply message

will be sent.

sent. (Actually, the kernel uses a send once right to send the exception

message, which <strong>thread_abort</strong> destroys, so replying to the message is harmless.)

The thread can always be destroyed with <strong>thread_terminate</strong>.

A thread can have two exception ports active for it: its thread type specific exception

port and the task type specific exception port. The kernel will try sending

an exception message to both ports looking for a reply message with a

return value of KERN_SUCCESS. The kernel tries the thread specific port first,

then the task specific port. If the return value from the first exception message

the kernel sends has a return value of KERN_SUCCESS, the thread continues

(with a possibly modified state). If the return value is not KERN_SUCCESS,

the kernel tries the second port. If that return value is KERN_SUCCESS, the

thread continues; otherwise, the thread is terminated.

To get the effect of a non-success return value, the server interface should return

MIG_DESTROY_REQUEST. This causes <strong>exc_server</strong> and <strong>mach_msg_server</strong>

to destroy the kernel's request (as opposed to sending a reply with a

KERN_SUCCESS value).

<h3>RETURN VALUES</h3>

A return value of KERN_SUCCESS indicates that the thread is to continue

from the point of exception. A return value of MIG_NO_REPLY indicates that

the exception was handled directly and the thread was restarted or terminated by

the exception handler. A return value of MIG_DESTROY_REQUEST causes

the kernel to try another exception handler (or terminate the thread). Any other

value will cause

<strong>mach_msg_server</strong> to remove the task and thread port references.

<h3>RELATED INFORMATION</h3>

Functions:

<a href="exc_server.html"><strong>exc_server</strong></a>,

<a href="thread_abort.html"><strong>thread_abort</strong></a>,

<a href="task_get_exception_ports.html"><strong>task_get_exception_ports</strong></a>,

<a href="thread_get_exception_ports.html"><strong>thread_get_exception_ports</strong></a>,

<a href="thread_get_state.html"><strong>thread_get_state</strong></a>,

<a href="thread_resume.html"><strong>thread_resume</strong></a>,

<a href="task_set_exception_ports.html"><strong>task_set_exception_ports</strong></a>,

<a href="thread_set_exception_ports.html"><strong>thread_set_exception_ports</strong></a>,

<a href="task_swap_exception_ports.html"><strong>task_swap_exception_ports</strong></a>,

<a href="TS_exception_ports.html"><strong>thread_swap_exception_ports</strong></a>,

<a href="thread_set_state.html"><strong>thread_set_state</strong></a>,

<a href="thread_suspend.html"><strong>thread_suspend</strong></a>,

<a href="thread_terminate.html"><strong>thread_terminate</strong></a>.