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Get __pthread_get_minstack at runtime with dlsym #23631

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Merged
merged 3 commits into from
Mar 24, 2015
Merged

Get __pthread_get_minstack at runtime with dlsym #23631

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0090e01
Get __pthread_get_minstack at runtime with dlsym
andersk Mar 23, 2015
b6641c1
min_stack_size: update non-Linux implementation comment
andersk Mar 23, 2015
737bb30
min_stack_size: clarify both reasons to use dlsym
andersk Mar 23, 2015
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40 changes: 26 additions & 14 deletions src/libstd/sys/unix/thread.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,12 +13,14 @@
use core::prelude::*;

use cmp;
use dynamic_lib::DynamicLibrary;
use ffi::CString;
use io;
use libc::consts::os::posix01::PTHREAD_STACK_MIN;
use libc;
use mem;
use ptr;
use sync::{Once, ONCE_INIT};
use sys::os;
use thunk::Thunk;
use time::Duration;
Expand Down Expand Up @@ -314,26 +316,36 @@ pub fn sleep(dur: Duration) {
// is created in an application with big thread-local storage requirements.
// See #6233 for rationale and details.
//
// Link weakly to the symbol for compatibility with older versions of glibc.
// Assumes that we've been dynamically linked to libpthread but that is
// currently always the case. Note that you need to check that the symbol
// is non-null before calling it!
// Use dlsym to get the symbol value at runtime, both for
// compatibility with older versions of glibc, and to avoid creating
// dependencies on GLIBC_PRIVATE symbols. Assumes that we've been
// dynamically linked to libpthread but that is currently always the
// case. We previously used weak linkage (under the same assumption),
// but that caused Debian to detect an unnecessarily strict versioned
// dependency on libc6 (#23628).
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since you're removing this could you merge the mac os implementation into this?

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I’m not a Mac user; does Rust use glibc on Mac? I figured we shouldn’t waste time looking up __pthread_get_minstack on non-glibc.

(But yeah, I should update the comment below, if nothing else.)

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i guess i'm not sure, just going by this comment: https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/thread.rs#L335

#[cfg(target_os = "linux")]
fn min_stack_size(attr: *const libc::pthread_attr_t) -> libc::size_t {
type F = unsafe extern "C" fn(*const libc::pthread_attr_t) -> libc::size_t;
extern {
#[linkage = "extern_weak"]
static __pthread_get_minstack: *const ();
}
if __pthread_get_minstack.is_null() {
PTHREAD_STACK_MIN
} else {
unsafe { mem::transmute::<*const (), F>(__pthread_get_minstack)(attr) }
static INIT: Once = ONCE_INIT;
static mut __pthread_get_minstack: Option<F> = None;

INIT.call_once(|| {
let lib = DynamicLibrary::open(None).unwrap();
unsafe {
if let Ok(f) = lib.symbol("__pthread_get_minstack") {
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nit: could use stringify!

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Nits are welcome. What’s the advantage of lib.symbol(stringify!(__pthread_get_minstack))? (Or do you mean something else?)

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just makes it explicit that the variable name matches the symbol name

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Does it? There’d still be nothing to check that they match. And the variable name isn’t really important; the important thing is that the symbol name matches the glibc name, which we can’t statically enforce.

__pthread_get_minstack = Some(mem::transmute::<*const (), F>(f));
}
}
});

match unsafe { __pthread_get_minstack } {
None => PTHREAD_STACK_MIN,
Some(f) => unsafe { f(attr) },
}
}

// __pthread_get_minstack() is marked as weak but extern_weak linkage is
// not supported on OS X, hence this kludge...
// No point in looking up __pthread_get_minstack() on non-glibc
// platforms.
#[cfg(not(target_os = "linux"))]
fn min_stack_size(_: *const libc::pthread_attr_t) -> libc::size_t {
PTHREAD_STACK_MIN
Expand Down