add linux sampler

components/background_hang_monitor/sampler_linux.rs

@@ -2,21 +2,136 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+#![allow(unsafe_code)]
+
 use crate::sampler::{NativeStack, Sampler};
 use libc;
+use nix::sys::signal::{sigaction, SaFlags, SigAction, SigHandler, SigSet, Signal};
+use std::cell::UnsafeCell;
+use std::io;
+use std::mem;
+use std::process;
+use std::thread;
 
-type MonitoredThreadId = libc::pthread_t;
+static mut SHARED_STATE: SharedState = SharedState {
+    msg2: None,
+    msg3: None,
+    msg4: None,
+    context: None,
+};
+
+type MonitoredThreadId = libc::pid_t;
+
+struct SharedState {
+    // "msg1" is the signal.
+    msg2: Option<PosixSemaphore>,
+    msg3: Option<PosixSemaphore>,
+    msg4: Option<PosixSemaphore>,
+    context: Option<libc::ucontext_t>,
+}
+
+fn clear_shared_state() {
+    unsafe {
+        SHARED_STATE.msg2 = None;
+        SHARED_STATE.msg3 = None;
+        SHARED_STATE.msg4 = None;
+        SHARED_STATE.context = None;
+    }
+}
+
+fn reset_shared_state() {
+    unsafe {
+        SHARED_STATE.msg2 = Some(PosixSemaphore::new(0).expect("valid semaphore"));
+        SHARED_STATE.msg3 = Some(PosixSemaphore::new(0).expect("valid semaphore"));
+        SHARED_STATE.msg4 = Some(PosixSemaphore::new(0).expect("valid semaphore"));
+        SHARED_STATE.context = None;
+    }
+}
+
+struct PosixSemaphore {
+    sem: UnsafeCell<libc::sem_t>,
+}
+
+impl PosixSemaphore {
+    pub fn new(value: u32) -> io::Result<Self> {
+        let mut sem: libc::sem_t = unsafe { mem::uninitialized() };
+        let r = unsafe {
+            libc::sem_init(&mut sem, 0 /* not shared */, value)
+        };
+        if r == -1 {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(PosixSemaphore {
+            sem: UnsafeCell::new(sem),
+        })
+    }
+
+    pub fn post(&self) -> io::Result<()> {
+        if unsafe { libc::sem_post(self.sem.get()) } == 0 {
+            Ok(())
+        } else {
+            Err(io::Error::last_os_error())
+        }
+    }
+
+    pub fn wait(&self) -> io::Result<()> {
+        if unsafe { libc::sem_wait(self.sem.get()) } == 0 {
+            Ok(())
+        } else {
+            Err(io::Error::last_os_error())
+        }
+    }
+
+    /// Retries the wait if it returned due to EINTR.
+    /// Returns Ok on success and the error on any other return value.
+    pub fn wait_through_intr(&self) -> io::Result<()> {
+        loop {
+            match self.wait() {
+                Err(os_error) => {
+                    let err = os_error.raw_os_error().expect("no os error");
+                    if err == libc::EINTR {
+                        thread::yield_now();
+                        continue;
+                    }
+                    return Err(os_error);
+                },
+                _ => return Ok(()),
+            }
+        }
+    }
+}
+
+unsafe impl Sync for PosixSemaphore {}
+
+impl Drop for PosixSemaphore {
+    /// Destroys the semaphore.
+    fn drop(&mut self) {
+        unsafe { libc::sem_destroy(self.sem.get()) };
+    }
+}
 
 #[allow(dead_code)]
 pub struct LinuxSampler {
     thread_id: MonitoredThreadId,
+    old_handler: SigAction,
 }
 
 impl LinuxSampler {
     #[allow(unsafe_code, dead_code)]
     pub fn new() -> Box<Sampler> {
-        let thread_id = unsafe { libc::pthread_self() };
-        Box::new(LinuxSampler { thread_id })
+        let thread_id = unsafe { libc::syscall(libc::SYS_gettid) as libc::pid_t };
+        let handler = SigHandler::SigAction(sigprof_handler);
+        let action = SigAction::new(
+            handler,
+            SaFlags::SA_RESTART | SaFlags::SA_SIGINFO,
+            SigSet::empty(),
+        );
+        let old_handler =
+            unsafe { sigaction(Signal::SIGPROF, &action).expect("signal handler set") };
+        Box::new(LinuxSampler {
+            thread_id,
+            old_handler,
+        })
     }
 }
 
@@ -28,8 +143,86 @@ impl Sampler for LinuxSampler {
         // we must not do any dynamic memory allocation,
         // nor try to acquire any lock
         // or any other unshareable resource.
+        // first we reinitialize the semaphores
+        reset_shared_state();
+
+        // signal the thread, wait for it to tell us state was copied.
+        send_sigprof(self.thread_id);
+        unsafe {
+            SHARED_STATE
+                .msg2
+                .as_ref()
+                .unwrap()
+                .wait_through_intr()
+                .expect("msg2 failed");
+        }
+
+        //let results = unsafe { callback(&mut SHARED_STATE.context.expect("valid context")) };
+
+        // signal the thread to continue.
+        unsafe {
+            SHARED_STATE
+                .msg3
+                .as_ref()
+                .unwrap()
+                .post()
+                .expect("msg3 failed");
+        }
+
+        // wait for thread to continue.
+        unsafe {
+            SHARED_STATE
+                .msg4
+                .as_ref()
+                .unwrap()
+                .wait_through_intr()
+                .expect("msg4 failed");
+        }
+
+        clear_shared_state();
 
         // NOTE: End of "critical section".
         Err(())
     }
 }
+
+impl Drop for LinuxSampler {
+    fn drop(&mut self) {
+        unsafe {
+            sigaction(Signal::SIGPROF, &self.old_handler).expect("previous signal handler restored")
+        };
+    }
+}
+
+extern "C" fn sigprof_handler(
+    sig: libc::c_int,
+    _info: *mut libc::siginfo_t,
+    ctx: *mut libc::c_void,
+) {
+    assert_eq!(sig, libc::SIGPROF);
+    unsafe {
+        // copy the context.
+        let context: libc::ucontext_t = *(ctx as *mut libc::ucontext_t);
+        SHARED_STATE.context = Some(context);
+        // Tell the sampler we copied the context.
+        SHARED_STATE.msg2.as_ref().unwrap().post().expect("posted");
+
+        // Wait for sampling to finish.
+        SHARED_STATE
+            .msg3
+            .as_ref()
+            .unwrap()
+            .wait_through_intr()
+            .expect("msg3 wait succeeded");
+
+        // OK we are done!
+        SHARED_STATE.msg4.as_ref().unwrap().post().expect("posted");
+        // DO NOT TOUCH shared state here onwards.
+    }
+}
+
+fn send_sigprof(to: libc::pid_t) {
+    unsafe {
+        libc::syscall(libc::SYS_tgkill, process::id(), to, libc::SIGPROF);
+    }
+}