1<h2>catch_exception_raise</h2>
2<hr>
3<p>
4<strong>Server Interface</strong> - Handles the occurrence of an exception within a thread.
5
6<h3>SYNOPSIS</h3>
7<pre>
8<strong>kern_return_t   catch_exception_raise</strong>
9                <strong>(mach_port_t</strong>                          <var>exception_port</var>,
10                 <strong>mach_port_t</strong>                                  <var>thread</var>,
11                 <strong>mach_port_t</strong>                                    <var>task</var>,
12                 <strong>exception_type_t</strong>                          <var>exception</var>,
13                 <strong>exception_data_t</strong>                               <var>code</var>,
14                 <strong>mach_msg_type_number_t</strong>                   <var>code_count</var><strong>);</strong>
15</pre>
16<p>
17<strong>catch_exception_raise_state</strong>
18expanded form:
19<pre>
20<strong>kern_return_t   catch_exception_raise_state</strong>
21                <strong>(mach_port_t</strong>                          <var>exception_port</var>,
22                 <strong>exception_type_t</strong>                          <var>exception</var>,
23                 <strong>exception_data_t</strong>                               <var>code</var>,
24                 <strong>mach_msg_type_number_t</strong>                   <var>code_count</var>,
25                 <strong>int *</strong>                                        <var>flavor</var>,
26                 <strong>thread_state_t</strong>                             <var>in_state</var>,
27                 <strong>mach_msg_type_number_t</strong>               <var>in_state_count</var>,
28                 <strong>thread_state_t</strong>                            <var>out_state</var>,
29                 <strong>mach_msg_type_number_t *</strong>            <var>out_state_count</var><strong>);</strong>
30</pre>
31<p>
32<strong>catch_exception_raise_state_identity</strong>
33expanded form:
34<pre>
35<strong>kern_return_t   catch_exception_raise_state_identity</strong>
36                <strong>(mach_port_t</strong>                          <var>exception_port</var>,
37                 <strong>mach_port_t</strong>                                  <var>thread</var>,
38                 <strong>mach_port_t</strong>                                    <var>task</var>,
39                 <strong>exception_type_t</strong>                          <var>exception</var>,
40                 <strong>exception_data_t</strong>                               <var>code</var>,
41                 <strong>mach_msg_type_number_t</strong>                   <var>code_count</var>,
42                 <strong>int *</strong>                                        <var>flavor</var>,
43                 <strong>thread_state_t</strong>                             <var>in_state</var>,
44                 <strong>mach_msg_type_number_t</strong>               <var>in_state_count</var>,
45                 <strong>thread_state_t</strong>                            <var>out_state</var>,
46                 <strong>mach_msg_type_number_t *</strong>            <var>out_state_count</var><strong>);</strong>
47</pre>
48<h3>PARAMETERS</h3>
49<dl>
50<dt> <var>exception_port</var>
51<dd>
52[in exception (receive) right] The port to which the exception
53notification was sent.
54<p>
55<dt> <var>thread</var>
56<dd>
57[in thread-self send right] The thread self port for the thread taking the 
58exception.
59<p>
60<dt> <var>task</var>
61<dd>
62[in task-self send right] The task self port for the task containing the 
63thread taking the exception.
64<p>
65<dt> <var>exception</var>
66<dd>
67[in scalar] The type of the exception.
68The machine independent values raised by all implementations are:
69     <dl>
70<p>
71<dt> EXC_BAD_ACCESS
72<dd>
73Could not access memory. subcode contains the bad memory 
74address.
75<p>
76<dt> EXC_BAD_INSTRUCTION
77<dd>
78Instruction failed. Illegal or undefined instruction or operand.
79<p>
80<dt> EXC_ARITHMETIC
81<dd>
82Arithmetic exception; exact nature of exception is in subcode 
83field.
84<p>
85<dt> EXC_EMULATION
86<dd>
87Emulation instruction. Emulation support instruction encountered.
88Details in subcode field.
89<p>
90<dt> EXC_SOFTWARE
91<dd>
92Software generated exception; exact exception is in subcode 
93field. Codes 0 - 0xFFFF reserved to hardware; codes 0x10000 
94- 0x1FFFF reserved for OS emulation.
95<p>
96<dt> EXC_BREAKPOINT
97<dd>
98Trace, breakpoint, etc. Details in subcode field.
99<p>
100<dt> EXC_SYSCALL
101<dd>
102System call requested. Details in subcode field.
103<p>
104<dt> EXC_MACH_SYSCALL
105<dd>
106System call with a number in the Mach call range requested. 
107Details in subcode field.
108     </dl
109<p>
110<dt> <var>code</var>
111<dd>
112[in scalar] A machine dependent array indicating a particular instance 
113of exception.
114<p>
115<dt> <var>code_count</var>
116<dd>
117[in scalar] The size of the buffer (in natural-sized units).
118<p>
119<dt> <var>flavor</var>
120<dd>
121[pointer to in/out scalar] On input, the type of state included as selected
122when the exception port was set. On output, the type of state being 
123returned.
124<p>
125<dt> <var>in_state</var>
126<dd>
127[pointer to in structure] State information of the thread at the time of 
128the exception.
129<p>
130<dt> <var>in_state_count</var>
131<dd>
132[in scalar] The size of the in state buffer (in natural-sized units).
133<p>
134<dt> <var>out_state</var>
135<dd>
136[out structure] The state the thread will have if continued from the 
137point of the exception. The maximum size of this array is 
138THREAD_STATE_MAX.
139<p>
140<dt> <var>out_state_count</var>
141<dd>
142[pointer to out scalar] The size of the out state buffer (in natural-sized units).
143     </dl>
144<h3>DESCRIPTION</h3>
145<p>
146A <strong>catch_exception_raise</strong> function is called by
147<strong>exc_server</strong> as the result of a
148kernel message indicating that an exception occurred within a thread. 
149The <var>exception_port</var> parameter specifies the port named via
150a previous call to <strong>thread_set_exception_ports</strong> or
151<strong>task_set_exception_ports</strong>
152as the port that responds when the thread takes an
153exception.
154<p>
155The alternate message forms (the format being selected when the exception port 
156was set) allow for selected thread state to be included.
157
158<h3>NOTES</h3>
159<p>
160When an exception occurs in a thread, the thread sends an exception message to 
161its exception port, blocking in the kernel waiting for the receipt of a reply. It is 
162assumed that some task is listening
163(most likely with <strong>mach_msg_server</strong>) to this 
164port, using the <strong>exc_server</strong> function
165to decode the messages and then call the 
166linked in <strong>catch_exception_raise</strong>.
167It is the job of <strong>catch_exception_raise</strong> to handle
168the exception and decide the course of action for thread.
169     <p>
170If the thread should continue from the point of exception, 
171<strong>catch_exception_raise</strong> would return KERN_SUCCESS. This causes a reply 
172message to be sent to the kernel, which will allow the thread to continue from 
173the point of the exception.
174If some other action should be taken by thread, the following actions should be 
175performed by <strong>catch_exception_raise</strong>:
176     <dl>
177       <dt> <strong>thread_suspend</strong>
178       <dd>
179		 This keeps the thread from proceeding after the next step.
180	    <p>
181<dt> <strong>thread_abort</strong>
182		 <dd>
183		  This aborts the message receive operation currently blocking 
184the thread.
185		      <p>
186<dt> <strong>thread_set_state</strong>
187     <dd>
188	  (if using the <strong>catch_exception_raise</strong> form). Set the 
189thread's state so that it continues doing something else.
190	  <p>
191	  <dt> <strong>thread_resume</strong>
192	       <dd>
193		    Let the thread start running from its new state.
194</dl>
195Returning a value other than KERN_SUCCESS insures that no reply message
196will be sent.
197sent. (Actually, the kernel uses a send once right to send the exception
198message, which <strong>thread_abort</strong> destroys, so replying to the message is harmless.)
199The thread can always be destroyed with <strong>thread_terminate</strong>.
200<p>
201A thread can have two exception ports active for it: its thread type specific exception
202port and the task type specific exception port. The kernel will try sending
203an exception message to both ports looking for a reply message with a 
204return value of KERN_SUCCESS. The kernel tries the thread specific port first, 
205then the task specific port. If the return value from the first exception message 
206the kernel sends has a return value of KERN_SUCCESS, the thread continues 
207(with a possibly modified state). If the return value is not KERN_SUCCESS, 
208the kernel tries the second port. If that return value is KERN_SUCCESS, the 
209thread continues; otherwise, the thread is terminated.
210<p>
211To get the effect of a non-success return value, the server interface should return 
212MIG_DESTROY_REQUEST. This causes <strong>exc_server</strong> and <strong>mach_msg_server</strong> 
213to destroy the kernel's request (as opposed to sending a reply with a 
214KERN_SUCCESS value).
215
216<h3>RETURN VALUES</h3>
217<p>
218A return value of KERN_SUCCESS indicates that the thread is to continue 
219from the point of exception. A return value of MIG_NO_REPLY indicates that 
220the exception was handled directly and the thread was restarted or terminated by 
221the exception handler. A return value of MIG_DESTROY_REQUEST causes 
222the kernel to try another exception handler (or terminate the thread). Any other 
223value will cause
224<strong>mach_msg_server</strong> to remove the task and thread port references.
225
226<h3>RELATED INFORMATION</h3>
227<p>
228Functions:
229<a href="exc_server.html"><strong>exc_server</strong></a>,
230<a href="thread_abort.html"><strong>thread_abort</strong></a>,
231<a href="task_get_exception_ports.html"><strong>task_get_exception_ports</strong></a>,
232<a href="thread_get_exception_ports.html"><strong>thread_get_exception_ports</strong></a>,
233<a href="thread_get_state.html"><strong>thread_get_state</strong></a>,
234<a href="thread_resume.html"><strong>thread_resume</strong></a>,
235<a href="task_set_exception_ports.html"><strong>task_set_exception_ports</strong></a>,
236<a href="thread_set_exception_ports.html"><strong>thread_set_exception_ports</strong></a>,
237<a href="task_swap_exception_ports.html"><strong>task_swap_exception_ports</strong></a>,
238<a href="TS_exception_ports.html"><strong>thread_swap_exception_ports</strong></a>,
239<a href="thread_set_state.html"><strong>thread_set_state</strong></a>,
240<a href="thread_suspend.html"><strong>thread_suspend</strong></a>,
241<a href="thread_terminate.html"><strong>thread_terminate</strong></a>.
242