Cache directory hierarchy (#217)

* Simple module compilation cache

* Fix base64 encoding bug

* Use warn! everywhere in cache system

* Remove unused import

* Temporary workaround for long path on Windows

* Remove unused import for non-windows builds

* Cache directory hierarchy

* Fix conditional compilation for debug mode

* Minor enhancements

wasmtime-environ/build.rs

@@ -0,0 +1,9 @@
+use std::process::Command;
+
+fn main() {
+    let git_rev = match Command::new("git").args(&["rev-parse", "HEAD"]).output() {
+        Ok(output) => String::from_utf8(output.stdout).unwrap(),
+        Err(_) => String::from("git-not-found"),
+    };
+    println!("cargo:rustc-env=GIT_REV={}", git_rev);
+}

wasmtime-environ/src/cache.rs

@@ -5,17 +5,15 @@ use cranelift_codegen::ir;
 use cranelift_codegen::isa;
 use directories::ProjectDirs;
 use lazy_static::lazy_static;
-use log::warn;
+use log::{debug, warn};
 use serde::de::{self, Deserialize, Deserializer, MapAccess, SeqAccess, Visitor};
 use serde::ser::{self, Serialize, SerializeSeq, SerializeStruct, Serializer};
-#[cfg(windows)]
 use std::ffi::OsString;
 use std::fmt;
 use std::fs;
 use std::io;
-#[cfg(windows)]
-use std::path::Path;
 use std::path::PathBuf;
+use std::string::{String, ToString};
 
 /// Module for configuring the cache system.
 pub mod conf {
@@ -48,29 +46,47 @@ lazy_static! {
             Some(proj_dirs) => {
                 let cache_dir = proj_dirs.cache_dir();
                 // Temporary workaround for: https://github.com/rust-lang/rust/issues/32689
-                #[cfg(windows)]
-                let mut long_path = OsString::from("\\\\?\\");
-                #[cfg(windows)]
-                let cache_dir = {
-                    if cache_dir.starts_with("\\\\?\\") {
-                        cache_dir
+                if cfg!(windows) {
+                    let mut long_path = OsString::new();
+                    if !cache_dir.starts_with("\\\\?\\") {
+                        long_path.push("\\\\?\\");
                     }
-                    else {
-                        long_path.push(cache_dir.as_os_str());
-                        Path::new(&long_path)
-                    }
-                };
-                match fs::create_dir_all(cache_dir) {
-                    Ok(()) => (),
-                    Err(err) => warn!("Unable to create cache directory, failed with: {}", err),
-                };
-                Some(cache_dir.to_path_buf())
+                    long_path.push(cache_dir.as_os_str());
+                    Some(PathBuf::from(long_path))
+                }
+                else {
+                    Some(cache_dir.to_path_buf())
+                }
             }
             None => {
-                warn!("Unable to find cache directory");
+                warn!("Failed to find proper cache directory location.");
                 None
             }
         };
+    static ref SELF_MTIME: String = {
+        match std::env::current_exe() {
+            Ok(path) => match fs::metadata(&path) {
+                Ok(metadata) => match metadata.modified() {
+                    Ok(mtime) => match mtime.duration_since(std::time::UNIX_EPOCH) {
+                        Ok(duration) => format!("{}", duration.as_millis()),
+                        Err(err) => format!("m{}", err.duration().as_millis()),
+                    },
+                    Err(_) => {
+                        warn!("Failed to get modification time of current executable");
+                        "no-mtime".to_string()
+                    }
+                },
+                Err(_) => {
+                    warn!("Failed to get metadata of current executable");
+                    "no-mtime".to_string()
+                }
+            },
+            Err(_) => {
+                warn!("Failed to get path of current executable");
+                "no-mtime".to_string()
+            }
+        }
+    };
 }
 
 pub struct ModuleCacheEntry {
@@ -87,14 +103,33 @@ pub struct ModuleCacheData {
 type ModuleCacheDataTupleType = (Compilation, Relocations, ModuleAddressMap);
 
 impl ModuleCacheEntry {
-    pub fn new(module: &Module, _isa: &dyn isa::TargetIsa, _generate_debug_info: bool) -> Self {
-        // TODO: cache directory hierarchy with isa name, compiler name & git revision, and files with flag if debug symbols are available
+    pub fn new(
+        module: &Module,
+        isa: &dyn isa::TargetIsa,
+        compiler_name: &str,
+        generate_debug_info: bool,
+    ) -> Self {
         let mod_cache_path = if conf::cache_enabled() {
             CACHE_DIR.clone().and_then(|p| {
                 module.hash.map(|hash| {
-                    p.join(format!(
-                        "mod-{}",
-                        base64::encode_config(&hash, base64::URL_SAFE_NO_PAD) // standard encoding uses '/' which can't be used for filename
+                    let compiler_dir = if cfg!(debug_assertions) {
+                        format!(
+                            "{comp_name}-{comp_ver}-{comp_mtime}",
+                            comp_name = compiler_name,
+                            comp_ver = env!("GIT_REV"),
+                            comp_mtime = *SELF_MTIME,
+                        )
+                    } else {
+                        format!(
+                            "{comp_name}-{comp_ver}",
+                            comp_name = compiler_name,
+                            comp_ver = env!("GIT_REV"),
+                        )
+                    };
+                    p.join(isa.name()).join(compiler_dir).join(format!(
+                        "mod-{mod_hash}{mod_dbg}",
+                        mod_hash = base64::encode_config(&hash, base64::URL_SAFE_NO_PAD), // standard encoding uses '/' which can't be used for filename
+                        mod_dbg = if generate_debug_info { ".d" } else { "" },
                     ))
                 })
             })
@@ -131,25 +166,46 @@ impl ModuleCacheEntry {
                     return;
                 }
             };
+            // Optimize syscalls: first, try writing to disk. It should succeed in most cases.
+            // Otherwise, try creating the cache directory and retry writing to the file.
             match fs::write(p, &cache_buf) {
                 Ok(()) => (),
                 Err(err) => {
-                    warn!(
-                        "Failed to write cached code to disk, path: {}, message: {}",
+                    debug!(
+                        "Attempting to create the cache directory, because \
+                         failed to write cached code to disk, path: {}, message: {}",
                         p.display(),
-                        err
+                        err,
                     );
-                    match fs::remove_file(p) {
-                        Ok(()) => (),
-                        Err(err) => {
-                            if err.kind() != io::ErrorKind::NotFound {
+                    let cache_dir = p.parent().unwrap();
+                    match fs::create_dir_all(cache_dir) {
+                        Ok(()) => match fs::write(p, &cache_buf) {
+                            Ok(()) => (),
+                            Err(err) => {
                                 warn!(
-                                    "Failed to cleanup invalid cache, path: {}, message: {}",
+                                    "Failed to write cached code to disk, path: {}, message: {}",
                                     p.display(),
                                     err
                                 );
+                                match fs::remove_file(p) {
+                                    Ok(()) => (),
+                                    Err(err) => {
+                                        if err.kind() != io::ErrorKind::NotFound {
+                                            warn!(
+                                                "Failed to cleanup invalid cache, path: {}, message: {}",
+                                                p.display(),
+                                                err
+                                            );
+                                        }
+                                    }
+                                }
                             }
-                        }
+                        },
+                        Err(err) => warn!(
+                            "Failed to create cache directory, path: {}, message: {}",
+                            cache_dir.display(),
+                            err
+                        ),
                     }
                 }
             }

wasmtime-environ/src/cranelift.rs

@@ -124,7 +124,7 @@ impl crate::compilation::Compiler for Cranelift {
         isa: &dyn isa::TargetIsa,
         generate_debug_info: bool,
     ) -> Result<(Compilation, Relocations, ModuleAddressMap), CompileError> {
-        let cache_entry = ModuleCacheEntry::new(module, isa, generate_debug_info);
+        let cache_entry = ModuleCacheEntry::new(module, isa, "cranelift", generate_debug_info);
 
         let data = match cache_entry.get_data() {
             Some(data) => data,