extendr_api/
thread_safety.rs

1//! Provide limited protection for multithreaded access to the R API.
2use crate::*;
3use extendr_ffi::{
4    R_MakeUnwindCont, R_UnwindProtect, Rboolean, Rf_error, Rf_protect, Rf_unprotect,
5};
6use std::cell::Cell;
7use std::sync::Mutex;
8
9/// A global lock, that should represent the global lock on the R-API.
10/// It is not tied to an actual instance of R.
11static R_API_LOCK: Mutex<()> = Mutex::new(());
12
13thread_local! {
14    static THREAD_HAS_LOCK: Cell<bool> = const { Cell::new(false) };
15}
16
17/// Run `f` while ensuring that `f` runs in a single-threaded manner.
18///
19/// This is intended for single-threaded access of the R's C-API.
20/// It is possible to have nested calls of `single_threaded` without deadlocking.
21///
22/// Note: This will fail badly if the called function `f` panics or calls `Rf_error`.
23pub fn single_threaded<F, R>(f: F) -> R
24where
25    F: FnOnce() -> R,
26{
27    let has_lock = THREAD_HAS_LOCK.with(|x| x.get());
28
29    // acquire R-API lock
30    let _guard = if !has_lock {
31        Some(R_API_LOCK.lock().unwrap())
32    } else {
33        None
34    };
35
36    // this thread now has the lock
37    THREAD_HAS_LOCK.with(|x| x.set(true));
38
39    let result = f();
40
41    // release the R-API lock
42    if _guard.is_some() {
43        THREAD_HAS_LOCK.with(|x| x.set(false));
44    }
45
46    result
47}
48
49static mut R_ERROR_BUF: Option<std::ffi::CString> = None;
50
51pub fn throw_r_error<S: AsRef<str>>(s: S) -> ! {
52    let s = s.as_ref();
53    unsafe {
54        R_ERROR_BUF = Some(std::ffi::CString::new(s).unwrap());
55        let ptr = std::ptr::addr_of!(R_ERROR_BUF);
56        Rf_error((*ptr).as_ref().unwrap().as_ptr());
57    };
58}
59
60/// Wrap an R function such as `Rf_findFunction` and convert errors and panics into results.
61/// ```ignore
62/// use extendr_api::prelude::*;
63/// test! {
64///    let res = catch_r_error(|| unsafe {
65///        throw_r_error("bad things!");
66///        std::ptr::null_mut()
67///    });
68///    assert_eq!(res.is_ok(), false);
69/// }
70/// ```
71pub fn catch_r_error<F>(f: F) -> Result<SEXP>
72where
73    F: FnOnce() -> SEXP + Copy,
74    F: std::panic::UnwindSafe,
75{
76    use std::os::raw;
77
78    unsafe extern "C" fn do_call<F>(data: *mut raw::c_void) -> SEXP
79    where
80        F: FnOnce() -> SEXP + Copy,
81    {
82        let data = data as *const ();
83        let f: &F = &*(data as *const F);
84        f()
85    }
86
87    unsafe extern "C" fn do_cleanup(_: *mut raw::c_void, jump: Rboolean) {
88        if jump != Rboolean::FALSE {
89            panic!("R has thrown an error.");
90        }
91    }
92
93    single_threaded(|| unsafe {
94        let fun_ptr = do_call::<F> as *const ();
95        let clean_ptr = do_cleanup as *const ();
96        let x = false;
97        let fun = std::mem::transmute::<
98            *const (),
99            Option<unsafe extern "C" fn(*mut std::ffi::c_void) -> *mut extendr_ffi::SEXPREC>,
100        >(fun_ptr);
101        let cleanfun = std::mem::transmute::<
102            *const (),
103            std::option::Option<unsafe extern "C" fn(*mut std::ffi::c_void, extendr_ffi::Rboolean)>,
104        >(clean_ptr);
105        let data = &f as *const _ as _;
106        let cleandata = &x as *const _ as _;
107        let cont = R_MakeUnwindCont();
108        Rf_protect(cont);
109
110        // Note that catch_unwind does not work for 32 bit windows targets.
111        let res = match std::panic::catch_unwind(|| {
112            R_UnwindProtect(fun, data, cleanfun, cleandata, cont)
113        }) {
114            Ok(res) => Ok(res),
115            Err(_) => Err("Error in protected R code".into()),
116        };
117        Rf_unprotect(1);
118        res
119    })
120}
121
122/// This function registers a configurable print panic hook, for use in extendr-based R-packages.
123/// If the environment variable `EXTENDR_BACKTRACE` is set to either `true` or `1`,
124/// then it displays the entire Rust panic traceback (default hook), otherwise it omits the panic backtrace.
125#[no_mangle]
126pub extern "C" fn register_extendr_panic_hook() {
127    static RUN_ONCE: std::sync::Once = std::sync::Once::new();
128    RUN_ONCE.call_once_force(|x| {
129        // just ignore repeated calls to this function
130        if x.is_poisoned() {
131            println!("warning: extendr panic hook info registration was done more than once");
132            return;
133        }
134        let default_hook = std::panic::take_hook();
135        std::panic::set_hook(Box::new(move |x| {
136            let show_traceback = std::env::var("EXTENDR_BACKTRACE")
137                .map(|v| v.eq_ignore_ascii_case("true") || v == "1")
138                .unwrap_or(false);
139            if show_traceback {
140                default_hook(x)
141            } else {
142                return;
143            }
144        }));
145    });
146}
extendr_api/thread_safety.rs

extendr_api/
thread_safety.rs
