1241370 - Don't strdup() the message name in InterruptFrame

Status: RESOLVED FIXED

(Core :: IPC, defect)

Description

[Nicholas Nethercote [inactive]]

I did some cumulative heap profiling with DMD. While playing an 8 minute video
on YouTube on Mac, 1.7% (438,000) of all calls to malloc were due to the
strdup() call in InterruptFrame()'s constructor. Those strings are only used in
IPC error messages.

The strings don't need to be strdup()'d because Message::name_ is always a
string literal:

- The Message() constructor that sets name_ is always passed a string literal
  (mostly in IPDL-generated code), or nothing, in which case "???" is
  used.

- Message::set_name() is also always passed a string literal (again, mostly in
  IPDL_generated code).

It would be nice if we could guarantee that it's always a string literal and
thus has the same lifetime as the program, but I don't think that's possible in
C++.

Also, the lifetime of InterruptFrame objects appears to be the same as that of
CxxStackFrame objects (because they're created in CxxStackFrame's ctor and
destroyed in CxxStackFrame's dtor), and CxxStackFrame is a stack-only class,
and it's always instantiated in a function that takes a |Message| as an
argument, so even if some of the names were not string literals I think the
lifetimes work out safely.

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: Don't strdup() the message name in InterruptFrame

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Comment on attachment 8710246 [details] [diff] [review]
Don't strdup() the message name in InterruptFrame

Review of attachment 8710246 [details] [diff] [review]:
-----------------------------------------------------------------

Also, we only ever use the string if we're about to crash :-). Nice find.

Comment 3

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/5d12e137f2c154dbbffb2cf9912709bcf9f594aa
Bug 1241370 - Don't strdup() the message name in InterruptFrame. r=billm.

Comment 4

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/5d12e137f2c1