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This makes proc_lib behaves like a normal process as far
as the propagation of exceptions is concerned.
Before this commit, the following difference could be
observed:
6> spawn_link(fun() -> ssl:send(a,b) end).
<0.43.0>
7> flush().
Shell got {'EXIT',<0.43.0>,
{function_clause,
[{ssl,send,[a,b],[{file,"..."},{line,275}]}]}}
ok
8> proc_lib:spawn_link(fun() -> ssl:send(a,b) end).
<0.46.0>
9> flush().
Shell got {'EXIT',<0.46.0>,function_clause}
After this commit, we get the following instead:
3> flush().
Shell got {'EXIT',<0.61.0>,
{function_clause,
[{ssl,send,[a,b],[{file,"..."},{line,275}]},
{proc_lib,init_p,3,[{file,"..."},{line,232}]}]}}
The stacktrace will show minor differences of course
but the form is now the same as without proc_lib.
The rationale behind this commit is that:
* We now have a single form regardless of how the process
was started
* We can use the stacktrace to programmatically alter behavior
(for example an HTTP server identifying problems in input
decoding to send back a generic 400, or a 500 otherwise)
* We can access the stacktrace to print it somewhere (for
example an HTTP server could send it back to the client
when a debug mode is enabled)
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The max_heap_size process flag can be used to limit the
growth of a process heap by killing it before it becomes
too large to handle. It is possible to set the maximum
using the `erl +hmax` option, `system_flag(max_heap_size, ...)`,
`spawn_opt(Fun, [{max_heap_size, ...}])` and
`process_flag(max_heap_size, ...)`.
It is possible to configure the behaviour of the process
when the maximum heap size is reached. The process may be
sent an untrappable exit signal with reason kill and/or
send an error_logger message with details on the process
state. A new trace event called gc_max_heap_size is
also triggered for the garbage_collection trace flag
when the heap grows larger than the configured size.
If kill and error_logger are disabled, it is still
possible to see that the maximum has been reached by
doing garbage collection tracing on the process.
The heap size is defined as the sum of the heap memory
that the process is currently using. This includes
all generational heaps, the stack, any messages that
are considered to be part of the heap and any extra
memory the garbage collector may need during collection.
In the current implementation this means that when a process
is set using on_heap message queue data mode, the messages
that are in the internal message queue are counted towards
this value. For off_heap, only matched messages count towards
the size of the heap. For mixed, it depends on race conditions
within the VM whether a message is part of the heap or not.
Below is an example run of the new behaviour:
Eshell V8.0 (abort with ^G)
1> f(P),P = spawn_opt(fun() -> receive ok -> ok end end, [{max_heap_size, 512}]).
<0.60.0>
2> erlang:trace(P, true, [garbage_collection, procs]).
1
3> [P ! lists:duplicate(M,M) || M <- lists:seq(1,15)],ok.
ok
4>
=ERROR REPORT==== 26-Apr-2016::16:25:10 ===
Process: <0.60.0>
Context: maximum heap size reached
Max heap size: 512
Total heap size: 723
Kill: true
Error Logger: true
GC Info: [{old_heap_block_size,0},
{heap_block_size,609},
{mbuf_size,145},
{recent_size,0},
{stack_size,9},
{old_heap_size,0},
{heap_size,211},
{bin_vheap_size,0},
{bin_vheap_block_size,46422},
{bin_old_vheap_size,0},
{bin_old_vheap_block_size,46422}]
flush().
Shell got {trace,<0.60.0>,gc_start,
[{old_heap_block_size,0},
{heap_block_size,233},
{mbuf_size,145},
{recent_size,0},
{stack_size,9},
{old_heap_size,0},
{heap_size,211},
{bin_vheap_size,0},
{bin_vheap_block_size,46422},
{bin_old_vheap_size,0},
{bin_old_vheap_block_size,46422}]}
Shell got {trace,<0.60.0>,gc_max_heap_size,
[{old_heap_block_size,0},
{heap_block_size,609},
{mbuf_size,145},
{recent_size,0},
{stack_size,9},
{old_heap_size,0},
{heap_size,211},
{bin_vheap_size,0},
{bin_vheap_block_size,46422},
{bin_old_vheap_size,0},
{bin_old_vheap_block_size,46422}]}
Shell got {trace,<0.60.0>,exit,killed}
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