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back: Limit the number of LLVM worker threads.
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michaelwoerister committed Feb 6, 2017
1 parent a3da24b commit fa0a728
Showing 1 changed file with 8 additions and 4 deletions.
12 changes: 8 additions & 4 deletions src/librustc_trans/back/write.rs
Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ use errors::emitter::Emitter;
use syntax_pos::MultiSpan;
use context::{is_pie_binary, get_reloc_model};

use std::cmp;
use std::ffi::CString;
use std::fs;
use std::path::{Path, PathBuf};
Expand Down Expand Up @@ -754,10 +755,13 @@ pub fn run_passes(sess: &Session,
}

// Process the work items, optionally using worker threads.
// NOTE: This code is not really adapted to incremental compilation where
// the compiler decides the number of codegen units (and will
// potentially create hundreds of them).
let num_workers = work_items.len() - 1;
// NOTE: We are hardcoding a limit of worker threads for now. With
// incremental compilation we can run into situations where we would
// open hundreds of threads otherwise -- which can make things slower
// if things don't fit into memory anymore, or can cause the compiler
// to crash because of too many open file handles. See #39280 for
// some discussion on how to improve this in the future.
let num_workers = cmp::min(work_items.len() - 1, 32);
if num_workers <= 1 {
run_work_singlethreaded(sess, &trans.exported_symbols, work_items);
} else {
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