std: Re-enable at_exit()

The new semantics of this function are that the callbacks are run when the *main
thread* exits, not when all threads have exited. This implies that other threads
may still be running when the `at_exit` callbacks are invoked and users need to
be prepared for this situation.

Users in the standard library have been audited in accordance to these new rules
as well.

Closes #20012

1 files changed, 11 insertions, 4 deletions

diff --git a/src/libstd/sys/unix/process.rs b/src/libstd/sys/unix/process.rs
index 835f4279d9b..48df8c4eced 100644
--- a/src/libstd/sys/unix/process.rs
+++ b/src/libstd/sys/unix/process.rs
@@ -11,7 +11,7 @@ use self::Req::*;
 
 use libc::{mod, pid_t, c_void, c_int};
 use c_str::CString;
-use io::{mod, IoResult, IoError, EndOfFile};
+use io::{IoResult, EndOfFile};
 use mem;
 use os;
 use ptr;
@@ -327,7 +327,7 @@ impl Process {
         // The actual communication between the helper thread and this thread is
         // quite simple, just a channel moving data around.
 
-        unsafe { HELPER.boot(register_sigchld, waitpid_helper) }
+        HELPER.boot(register_sigchld, waitpid_helper);
 
         match self.try_wait() {
             Some(ret) => return Ok(ret),
@@ -335,7 +335,7 @@ impl Process {
         }
 
         let (tx, rx) = channel();
-        unsafe { HELPER.send(NewChild(self.pid, tx, deadline)); }
+        HELPER.send(NewChild(self.pid, tx, deadline));
         return match rx.recv_opt() {
             Ok(e) => Ok(e),
             Err(()) => Err(timeout("wait timed out")),
@@ -419,8 +419,15 @@ impl Process {
                             Ok(NewChild(pid, tx, deadline)) => {
                                 active.push((pid, tx, deadline));
                             }
+                            // Once we've been disconnected it means the main
+                            // thread is exiting (at_exit has run). We could
+                            // still have active waiter for other threads, so
+                            // we're just going to drop them all on the floor.
+                            // This means that they won't receive a "you're
+                            // done" message in which case they'll be considered
+                            // as timed out, but more generally errors will
+                            // start propagating.
                             Err(comm::Disconnected) => {
-                                assert!(active.len() == 0);
                                 break 'outer;
                             }
                             Err(comm::Empty) => break,