Process repositories on multiple threads

Use 'rayon' to parallelise the repository processing. Each repository is
processed in a thread in the default 'rayon' pool.

In order to get thread-safe access to the database, I followed some
advice from a Stack Overflow answer by VasiliNovikov
(https://stackoverflow.com/users/1091436/vasilinovikov):
https://stackoverflow.com/questions/62560396/how-to-use-sqlite-via-rusqlite-from-multiple-threads/62560397#62560397

VasiliNovikov recommended creating a database connection pool using
'r2d2_sqlite'. This way we don't have to share a database connection
between threads, but each thread can have its own connection.

This also means we can remove mutable requirements in a bunch of places
involving our `database::Db` type since we're no longer managing the
database connections directly.

1 files changed, 3 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index c56b025..6e61a17 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,6 +11,9 @@ filetime = "0.2.14"
 getopts = "0.2.21"
 git2 = "0.13.20"
 parse-size = { version = "1.0.0", features = ["std"] }
+r2d2 = "0.8.9"
+r2d2_sqlite = "0.18.0"
+rayon = "1.5.1"
 rusqlite = "0.25.3"
 serde = { version = "1.0.126", features = ["derive"] }
 thiserror = "1.0.25"