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    //! A library for acquiring a backtrace at runtime
    //!
    //! This library is meant to supplement the `RUST_BACKTRACE=1` support of the
    //! standard library by allowing an acquisition of a backtrace at runtime
    //! programmatically. The backtraces generated by this library do not need to be
    //! parsed, for example, and expose the functionality of multiple backend
    //! implementations.
    //!
    //! # Implementation
    //!
    //! This library makes use of a number of strategies for actually acquiring a
    //! backtrace. For example unix uses libgcc's libunwind bindings by default to
    //! acquire a backtrace, but coresymbolication or dladdr is used on OSX to
    //! acquire symbol names while linux uses gcc's libbacktrace.
    //!
    //! When using the default feature set of this library the "most reasonable" set
    //! of defaults is chosen for the current platform, but the features activated
    //! can also be controlled at a finer granularity.
    //!
    //! # Platform Support
    //!
    //! Currently this library is verified to work on Linux, OSX, and Windows, but
    //! it may work on other platforms as well. Note that the quality of the
    //! backtrace may vary across platforms.
    //!
    //! # API Principles
    //!
    //! This library attempts to be as flexible as possible to accommodate different
    //! backend implementations of acquiring a backtrace. Consequently the currently
    //! exported functions are closure-based as opposed to the likely expected
    //! iterator-based versions. This is done due to limitations of the underlying
    //! APIs used from the system.
    //!
    //! # Usage
    //!
    //! First, add this to your Cargo.toml
    //!
    //! ```toml
    //! [dependencies]
    //! backtrace = "0.2"
    //! ```
    //!
    //! Next:
    //!
    //! ```
    //! extern crate backtrace;
    //!
    //! fn main() {
    //!     backtrace::trace(|frame| {
    //!         let ip = frame.ip();
    //!         let symbol_address = frame.symbol_address();
    //!
    //!         // Resolve this instruction pointer to a symbol name
    //!         backtrace::resolve(ip, |symbol| {
    //!             if let Some(name) = symbol.name() {
    //!                 // ...
    //!             }
    //!             if let Some(filename) = symbol.filename() {
    //!                 // ...
    //!             }
    //!         });
    //!
    //!         true // keep going to the next frame
    //!     });
    //! }
    //! ```

    #![doc(html_root_url = "http://alexcrichton.com/backtrace-rs")]
    #![deny(missing_docs)]
    #![deny(warnings)]

    #[cfg(unix)]
    extern crate libc;
    #[cfg(all(windows, feature = "winapi"))] extern crate winapi;

    #[cfg(feature = "serde_derive")]
    #[cfg_attr(feature = "serde_derive", macro_use)]
    extern crate serde_derive;

    #[cfg(feature = "rustc-serialize")]
    extern crate rustc_serialize;

    #[macro_use]
    extern crate cfg_if;

    extern crate rustc_demangle;

    #[cfg(feature = "cpp_demangle")]
    extern crate cpp_demangle;

    #[cfg(all(feature = "gimli-symbolize",
              unix,
              target_os = "linux"))]
    extern crate addr2line;
    #[cfg(all(feature = "gimli-symbolize",
              unix,
              target_os = "linux"))]
    extern crate findshlibs;

    #[allow(dead_code)] // not used everywhere
    #[cfg(unix)]
    #[macro_use]
    mod dylib;

    pub use backtrace::{trace, Frame};
    mod backtrace;

    pub use symbolize::{resolve, Symbol, SymbolName};
    mod symbolize;

    pub use capture::{Backtrace, BacktraceFrame, BacktraceSymbol};
    mod capture;

    #[allow(dead_code)]
    struct Bomb {
        enabled: bool,
    }

    #[allow(dead_code)]
    impl Drop for Bomb {
        fn drop(&mut self) {
            if self.enabled {
                panic!("cannot panic during the backtrace function");
            }
        }
    }

    #[allow(dead_code)]
    mod lock {
        use std::cell::Cell;
        use std::mem;
        use std::sync::{Once, Mutex, MutexGuard, ONCE_INIT};

        pub struct LockGuard(MutexGuard<'static, ()>);

        static mut LOCK: *mut Mutex<()> = 0 as *mut _;
        static INIT: Once = ONCE_INIT;
        thread_local!(static LOCK_HELD: Cell<bool> = Cell::new(false));

        impl Drop for LockGuard {
            fn drop(&mut self) {
                LOCK_HELD.with(|slot| {
                    assert!(slot.get());
                    slot.set(false);
                });
            }
        }

        pub fn lock() -> Option<LockGuard> {
            if LOCK_HELD.with(|l| l.get()) {
                return None
            }
            LOCK_HELD.with(|s| s.set(true));
            unsafe {
                INIT.call_once(|| {
                    LOCK = mem::transmute(Box::new(Mutex::new(())));
                });
                Some(LockGuard((*LOCK).lock().unwrap()))
            }
        }
    }

    // requires external synchronization
    #[cfg(all(windows, feature = "dbghelp"))]
    unsafe fn dbghelp_init() {
        use winapi::shared::minwindef;
        use winapi::um::{dbghelp, processthreadsapi};

        static mut INITIALIZED: bool = false;

        if !INITIALIZED {
            dbghelp::SymInitializeW(processthreadsapi::GetCurrentProcess(),
                                    0 as *mut _,
                                    minwindef::TRUE);
            INITIALIZED = true;
        }
    }

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