Collector refactoring and multithreaded search (#437)

* Split Collector into an overall Collector and a per-segment SegmentCollector. Precursor to cross-segment parallelism, and as a side benefit cleans up any per-segment fields from being Option<T> to just T.

* Attempt to add MultiCollector back

* working. Chained collector is broken though

* Fix chained collector

* Fix test

* Make Weight Send+Sync for parallelization purposes

* Expose parameters of RangeQuery for external usage

* Removed &mut self

* fixing tests

* Restored TestCollectors

* blop

* multicollector working

* chained collector working

* test broken

* fixing unit test

* blop

* blop

* Blop

* simplifying APi

* blop

* better syntax

* Simplifying top_collector

* refactoring

* blop

* Sync with master

* Added multithread search

* Collector refactoring

* Schema::builder

* CR and rustdoc

* CR comments

* blop

* Added an executor

* Sorted the segment readers in the searcher

* Update searcher.rs

* Fixed unit testst

* changed the place where we have the sort-segment-by-count heuristic

* using crossbeam::channel

* inlining

* Comments about panics propagating

* Added unit test for executor panicking

* Readded default

* Removed Default impl

* Added unit test for executor

1 files changed, 13 insertions, 12 deletions

diff --git a/src/error.rs b/src/error.rs
index c651ad7..5fe3071 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -15,13 +15,13 @@ use std::sync::PoisonError;
 #[derive(Debug, Fail)]
 pub enum TantivyError {
     /// Path does not exist.
-    #[fail(display = "path does not exist: '{:?}'", _0)]
+    #[fail(display = "Path does not exist: '{:?}'", _0)]
     PathDoesNotExist(PathBuf),
     /// File already exists, this is a problem when we try to write into a new file.
-    #[fail(display = "file already exists: '{:?}'", _0)]
+    #[fail(display = "File already exists: '{:?}'", _0)]
     FileAlreadyExists(PathBuf),
     /// Index already exists in this directory
-    #[fail(display = "index already exists")]
+    #[fail(display = "Index already exists")]
     IndexAlreadyExists,
     /// Failed to acquire file lock
     #[fail(
@@ -30,28 +30,29 @@ pub enum TantivyError {
     )]
     LockFailure(LockType),
     /// IO Error.
-    #[fail(display = "an IO error occurred: '{}'", _0)]
+    #[fail(display = "An IO error occurred: '{}'", _0)]
     IOError(#[cause] IOError),
-    /// The data within is corrupted.
-    ///
-    /// For instance, it contains invalid JSON.
-    #[fail(display = "file contains corrupted data: '{:?}'", _0)]
+    /// Data corruption.
+    #[fail(display = "File contains corrupted data: '{:?}'", _0)]
     CorruptedFile(PathBuf),
     /// A thread holding the locked panicked and poisoned the lock.
-    #[fail(display = "a thread holding the locked panicked and poisoned the lock")]
+    #[fail(display = "A thread holding the locked panicked and poisoned the lock")]
     Poisoned,
     /// Invalid argument was passed by the user.
-    #[fail(display = "an invalid argument was passed: '{}'", _0)]
+    #[fail(display = "An invalid argument was passed: '{}'", _0)]
     InvalidArgument(String),
     /// An Error happened in one of the thread.
-    #[fail(display = "an error occurred in a thread: '{}'", _0)]
+    #[fail(display = "An error occurred in a thread: '{}'", _0)]
     ErrorInThread(String),
     /// An Error appeared related to the schema.
     #[fail(display = "Schema error: '{}'", _0)]
     SchemaError(String),
     /// Tried to access a fastfield reader for a field not configured accordingly.
-    #[fail(display = "fast field not available: '{:?}'", _0)]
+    #[fail(display = "Fast field not available: '{:?}'", _0)]
     FastFieldError(#[cause] FastFieldNotAvailableError),
+    /// System error. (e.g.: We failed spawning a new thread)
+    #[fail(display = "System error.'{}'", _0)]
+    SystemError(String),
 }
 
 impl From<FastFieldNotAvailableError> for TantivyError {