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std: Make logging safely implemented

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This commit fixes the logging function to be safely implemented, as well as
forcibly requiring a task to be present to use logging macros. This is safely
implemented by transferring ownership of the logger from the task to the local
stack frame in order to perform the print. This means that if a logger does more
logging while logging a new one will be initialized and then will get
overwritten once the initial logging function returns.

Without a scheme such as this, it is possible to unsafely alias two loggers by
logging twice (unsafely borrows from the task twice).
This commit is contained in:
Alex Crichton 2013-12-12 17:34:29 -08:00
parent dd19785f96
commit 76270816d5
1 changed files with 11 additions and 21 deletions
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32
src/libstd/logging.rs
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@ -118,26 +118,16 @@ pub static ERROR: u32 = 1;
/// It is not recommended to call this function directly, rather it should be
/// invoked through the logging family of macros.
pub fn log(_level: u32, args: &fmt::Arguments) {
unsafe {
let optional_task: Option<*mut Task> = Local::try_unsafe_borrow();
match optional_task {
Some(local) => {
// Lazily initialize the local task's logger
match (*local).logger {
// Use the available logger if we have one
Some(ref mut logger) => { logger.log(args); }
None => {
let mut logger = StdErrLogger::new();
logger.log(args);
(*local).logger = Some(logger);
}
}
}
// If there's no local task, then always log to stderr
None => {
let mut logger = StdErrLogger::new();
logger.log(args);
}
}
let mut logger = {
let mut task = Local::borrow(None::<Task>);
task.get().logger.take()
};
if logger.is_none() {
logger = Some(StdErrLogger::new());
}
logger.get_mut_ref().log(args);
let mut task = Local::borrow(None::<Task>);
task.get().logger = logger;
}