Write some crate level documentation

measureme/src/lib.rs

@@ -1,3 +1,52 @@
+//! This crate provides a library for high-performance event tracing which is used by the Rust compiler's unstable `-Z self-profile` feature.
+//!
+//! There are two main parts to this library:
+//! - Writing event trace files
+//! - Reading event trace files
+//!
+//! The output of a tracing session will be three files:
+//! 1. A `.events` file which contains all of the traced events.
+//! 2. A `.string_data` file which contains all the strings referenced by events.
+//! 3. A `.string_index` file which maps `StringId` values to offsets into the `.string_data` file.
+//!
+//! # Writing event trace files
+//!
+//! The main entry point for writing event trace files is the [`Profiler`] struct.
+//!
+//! To create a [`Profiler`], call the [`Profiler::new()`] function and provide a `Path` with the directory and file name for the trace files.
+//!
+//! To record an event, call the [`Profiler::record_event()`] method, passing a few arguments:
+//! - `event_kind`: a [`StringId`] which assigns an arbitrary category to the event
+//! - `event_id`: a [`StringId`] which specifies the name of the event
+//! - `thread_id`: a `u64` id of the thread which is recording this event
+//! - `timestamp_kind`: a [`TimestampKind`] which specifies how this event should be treated by `measureme` tooling
+//!
+//! To create a [`StringId`], call one of the string allocation methods:
+//! - [`Profiler::alloc_string()`]: allocates a string and returns the [`StringId`] that refers to it
+//! - [`Profiler::alloc_string_with_reserved_id()`]: allocates a string using the specified [`StringId`].
+//! It is up to the caller to make sure the specified [`StringId`] hasn't already been used.
+//!
+//! # Reading event trace files
+//!
+//! The main entry point for reading trace files is the [`ProfilingData`] struct.
+//!
+//! To create a [`ProfilingData`], call the [`ProfilingData::new()`] function and provide a `Path` with the directory and file name for the trace files.
+//!
+//! To retrieve an `Iterator` of all of the events in the file, call the [`ProfilingData::iter()`] method.
+//!
+//! To retrieve an `Iterator` of only matching start/stop events, call the [`ProfilingData::iter_matching_events()`] method.
+//!
+//! [`Profiler`]: struct.Profiler.html
+//! [`Profiler::alloc_string()`]: struct.Profiler.html#method.alloc_string
+//! [`Profiler::alloc_string_with_reserved_id()`]: struct.Profiler.html#method.alloc_string_with_reserved_id
+//! [`Profiler::new()`]: struct.Profiler.html#method.new
+//! [`Profiler::record_event()`]: struct.Profiler.html#method.record_event
+//! [`ProfilingData`]: struct.ProfilingData.html
+//! [`ProfilingData::iter()`]: struct.ProfilingData.html#method.iter
+//! [`ProfilingData::iter_matching_events()`]: struct.ProfilingData.html#method.iter_matching_events
+//! [`StringId`]: struct.StringId.html
+//! [`TimestampKind`]: enum.TimestampKind.html
+
 mod event;
 mod file_header;
 #[cfg(any(not(target_arch = "wasm32"), target_os = "wasi"))]