#
cargo/core/compiler/job_queue/
job_state.rs

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    //! See [`JobState`].

    use std::{cell::Cell, marker, sync::Arc};

    use cargo_util::ProcessBuilder;

    use crate::core::compiler::build_runner::OutputFile;
    use crate::core::compiler::future_incompat::FutureBreakageItem;
    use crate::util::Queue;
    use crate::CargoResult;

    use super::{Artifact, DiagDedupe, Job, JobId, Message};

    /// A `JobState` is constructed by `JobQueue::run` and passed to `Job::run`. It includes everything
    /// necessary to communicate between the main thread and the execution of the job.
    ///
    /// The job may execute on either a dedicated thread or the main thread. If the job executes on the
    /// main thread, the `output` field must be set to prevent a deadlock.
    pub struct JobState<'a, 'gctx> {
        /// Channel back to the main thread to coordinate messages and such.
        ///
        /// When the `output` field is `Some`, care must be taken to avoid calling `push_bounded` on
        /// the message queue to prevent a deadlock.
        messages: Arc<Queue<Message>>,

        /// Normally output is sent to the job queue with backpressure. When the job is fresh
        /// however we need to immediately display the output to prevent a deadlock as the
        /// output messages are processed on the same thread as they are sent from. `output`
        /// defines where to output in this case.
        ///
        /// Currently the [`Shell`] inside [`GlobalContext`] is wrapped in a `RefCell` and thus can't
        /// be passed between threads. This means that it isn't possible for multiple output messages
        /// to be interleaved. In the future, it may be wrapped in a `Mutex` instead. In this case
        /// interleaving is still prevented as the lock would be held for the whole printing of an
        /// output message.
        ///
        /// [`Shell`]: crate::core::Shell
        /// [`GlobalContext`]: crate::GlobalContext
        output: Option<&'a DiagDedupe<'gctx>>,

        /// The job id that this state is associated with, used when sending
        /// messages back to the main thread.
        id: JobId,

        /// Whether or not we're expected to have a call to `rmeta_produced`. Once
        /// that method is called this is dynamically set to `false` to prevent
        /// sending a double message later on.
        rmeta_required: Cell<bool>,

        // Historical versions of Cargo made use of the `'a` argument here, so to
        // leave the door open to future refactorings keep it here.
        _marker: marker::PhantomData<&'a ()>,
    }

    impl<'a, 'gctx> JobState<'a, 'gctx> {
        pub(super) fn new(
            id: JobId,
            messages: Arc<Queue<Message>>,
            output: Option<&'a DiagDedupe<'gctx>>,
            rmeta_required: bool,
        ) -> Self {
            Self {
                id,
                messages,
                output,
                rmeta_required: Cell::new(rmeta_required),
                _marker: marker::PhantomData,
            }
        }

        pub fn running(&self, cmd: &ProcessBuilder) {
            self.messages.push(Message::Run(self.id, cmd.to_string()));
        }

        pub fn build_plan(
            &self,
            module_name: String,
            cmd: ProcessBuilder,
            filenames: Arc<Vec<OutputFile>>,
        ) {
            self.messages
                .push(Message::BuildPlanMsg(module_name, cmd, filenames));
        }

        pub fn stdout(&self, stdout: String) -> CargoResult<()> {
            if let Some(dedupe) = self.output {
                writeln!(dedupe.gctx.shell().out(), "{}", stdout)?;
            } else {
                self.messages.push_bounded(Message::Stdout(stdout));
            }
            Ok(())
        }

        pub fn stderr(&self, stderr: String) -> CargoResult<()> {
            if let Some(dedupe) = self.output {
                let mut shell = dedupe.gctx.shell();
                shell.print_ansi_stderr(stderr.as_bytes())?;
                shell.err().write_all(b"\n")?;
            } else {
                self.messages.push_bounded(Message::Stderr(stderr));
            }
            Ok(())
        }

        /// See [`Message::Diagnostic`] and [`Message::WarningCount`].
        pub fn emit_diag(&self, level: &str, diag: String, fixable: bool) -> CargoResult<()> {
            if let Some(dedupe) = self.output {
                let emitted = dedupe.emit_diag(&diag)?;
                if level == "warning" {
                    self.messages.push(Message::WarningCount {
                        id: self.id,
                        emitted,
                        fixable,
                    });
                }
            } else {
                self.messages.push_bounded(Message::Diagnostic {
                    id: self.id,
                    level: level.to_string(),
                    diag,
                    fixable,
                });
            }
            Ok(())
        }

        /// See [`Message::Warning`].
        pub fn warning(&self, warning: String) -> CargoResult<()> {
            self.messages.push_bounded(Message::Warning {
                id: self.id,
                warning,
            });
            Ok(())
        }

        /// A method used to signal to the coordinator thread that the rmeta file
        /// for an rlib has been produced. This is only called for some rmeta
        /// builds when required, and can be called at any time before a job ends.
        /// This should only be called once because a metadata file can only be
        /// produced once!
        pub fn rmeta_produced(&self) {
            self.rmeta_required.set(false);
            self.messages
                .push(Message::Finish(self.id, Artifact::Metadata, Ok(())));
        }

        /// Drives a [`Job`] to finish. This ensures that a [`Message::Finish`] is
        /// sent even if our job panics.
        pub(super) fn run_to_finish(self, job: Job) {
            let mut sender = FinishOnDrop {
                messages: &self.messages,
                id: self.id,
                result: None,
            };
            sender.result = Some(job.run(&self));

            // If the `rmeta_required` wasn't consumed but it was set
            // previously, then we either have:
            //
            // 1. The `job` didn't do anything because it was "fresh".
            // 2. The `job` returned an error and didn't reach the point where
            //    it called `rmeta_produced`.
            // 3. We forgot to call `rmeta_produced` and there's a bug in Cargo.
            //
            // Ruling out the third, the other two are pretty common for 2
            // we'll just naturally abort the compilation operation but for 1
            // we need to make sure that the metadata is flagged as produced so
            // send a synthetic message here.
            if self.rmeta_required.get() && sender.result.as_ref().unwrap().is_ok() {
                self.messages
                    .push(Message::Finish(self.id, Artifact::Metadata, Ok(())));
            }

            // Use a helper struct with a `Drop` implementation to guarantee
            // that a `Finish` message is sent even if our job panics. We
            // shouldn't panic unless there's a bug in Cargo, so we just need
            // to make sure nothing hangs by accident.
            struct FinishOnDrop<'a> {
                messages: &'a Queue<Message>,
                id: JobId,
                result: Option<CargoResult<()>>,
            }

            impl Drop for FinishOnDrop<'_> {
                fn drop(&mut self) {
                    let result = self
                        .result
                        .take()
                        .unwrap_or_else(|| Err(anyhow::format_err!("worker panicked")));
                    self.messages
                        .push(Message::Finish(self.id, Artifact::All, result));
                }
            }
        }

        pub fn future_incompat_report(&self, report: Vec<FutureBreakageItem>) {
            self.messages
                .push(Message::FutureIncompatReport(self.id, report));
        }
    }