Merge pull request #56 from blas-lapack-rs/openblas-build-cache

Support cache feature for openblas-build

Author: termoshtt

openblas-build/src/build.rs

@@ -22,14 +22,14 @@ fn openblas_source_dir() -> PathBuf {
 }
 
 /// Interface for 32-bit interger (LP64) and 64-bit integer (ILP64)
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Interface {
     LP64,
     ILP64,
 }
 
 /// CPU list in [TargetList](https://github.com/xianyi/OpenBLAS/blob/v0.3.10/TargetList.txt)
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 #[allow(non_camel_case_types)] // to use original identifiers
 pub enum Target {
     // X86/X86_64 Intel
@@ -129,7 +129,7 @@ pub enum Target {
 }
 
 /// make option generator
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Configure {
     pub no_static: bool,
     pub no_shared: bool,

openblas-src/Cargo.toml

@@ -46,6 +46,9 @@ system = []
 [dev-dependencies]
 libc = "0.2"
 
+[build-dependencies]
+dirs = "3.0.1"
+
 [target.'cfg(target_os="windows")'.build-dependencies]
 vcpkg = "0.2"
 

openblas-src/build.rs

@@ -94,7 +94,6 @@ fn main() {
 /// Build OpenBLAS using openblas-build crate
 #[cfg(target_os = "linux")]
 fn build() {
-    let output = PathBuf::from(env::var("OUT_DIR").unwrap());
     let mut cfg = openblas_build::Configure::default();
     if !feature_enabled("cblas") {
         cfg.no_cblas = true;
@@ -107,6 +106,46 @@ fn build() {
     } else {
         cfg.no_static = true;
     }
+
+    let output = if feature_enabled("cache") {
+        use std::{collections::hash_map::DefaultHasher, hash::*};
+        // Build OpenBLAS on user's data directory.
+        // See https://docs.rs/dirs/3.0.1/dirs/fn.data_dir.html
+        //
+        // On Linux, `data_dir` returns `$XDG_DATA_HOME` or `$HOME/.local/share`.
+        // This build script creates a directory based on the hash value of `cfg`,
+        // i.e. `$XDG_DATA_HOME/openblas_build/[Hash of cfg]`, and build OpenBLAS there.
+        //
+        // This build will be shared among several projects using openblas-src crate.
+        // It makes users not to build OpenBLAS in every `cargo build`.
+        let mut hasher = DefaultHasher::new();
+        cfg.hash(&mut hasher);
+        let output = dirs::data_dir()
+            .expect("Cannot get user's data directory")
+            .join("openblas_build")
+            .join(format!("{:x}", hasher.finish()));
+        output
+    } else {
+        PathBuf::from(env::var("OUT_DIR").unwrap())
+    };
+
+    // If OpenBLAS is build as shared, user of openblas-src will have to find `libopenblas.so` at runtime.
+    //
+    // `cargo run` appends the link paths to `LD_LIBRARY_PATH` specified by `cargo:rustc-link-search`,
+    // and user's crate can find it then.
+    //
+    // However, when user try to run it directly like `./target/release/user_crate_exe`, it will say
+    // "error while loading shared libraries: libopenblas.so: cannot open shared object file: No such file or directory".
+    //
+    // Be sure that `cargo:warning` is shown only when openblas-src is build as path dependency...
+    // https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargowarningmessage
+    if !feature_enabled("static") {
+        println!(
+            "cargo:warning=OpenBLAS is built as a shared library. You need to set LD_LIBRARY_PATH={}",
+            output.display()
+        );
+    }
+
     let deliv = cfg.build(&output).unwrap();
 
     for search_path in &deliv.make_conf.c_extra_libs.search_paths {