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Handle buffer changes made by a handler of the OnIdle event #4442

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Merged
merged 3 commits into from
Feb 4, 2025
Merged

Handle buffer changes made by a handler of the OnIdle event #4442

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4e4aec0
Handle buffer changes made by OnIdle event handler
daxian-dbw Feb 2, 2024
7db02f2
Insert text using the OnIdle event
daxian-dbw Jan 7, 2025
6e1297d
minor update
daxian-dbw Feb 3, 2025
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1 change: 1 addition & 0 deletions PSReadLine/PublicAPI.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,7 @@ public static void Insert(char c)
/// <param name="s">String to insert</param>
public static void Insert(string s)
{
s = s.Replace("\r\n", "\n");
_singleton.SaveEditItem(EditItemInsertString.Create(s, _singleton._current));

// Use Append if possible because Insert at end makes StringBuilder quite slow.
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50 changes: 38 additions & 12 deletions PSReadLine/ReadLine.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,7 @@ internal static PSKeyInfo ReadKey()
// If we timed out, check for event subscribers (which is just
// a hint that there might be an event waiting to be processed.)
var eventSubscribers = _singleton._engineIntrinsics?.Events.Subscribers;
int bufferLen = _singleton._buffer.Length;
if (eventSubscribers?.Count > 0)
{
bool runPipelineForEventProcessing = false;
Expand All @@ -211,16 +212,20 @@ internal static PSKeyInfo ReadKey()
if (string.Equals(sub.SourceIdentifier, PSEngineEvent.OnIdle, StringComparison.OrdinalIgnoreCase))
{
// If the buffer is not empty, let's not consider we are idle because the user is in the middle of typing something.
if (_singleton._buffer.Length > 0)
if (bufferLen > 0)
{
continue;
}

// There is an OnIdle event subscriber and we are idle because we timed out and the buffer is empty.
// Normally PowerShell generates this event, but PowerShell assumes the engine is not idle because
// it called PSConsoleHostReadLine which isn't returning. So we generate the event instead.
// There is an 'OnIdle' event subscriber and we are idle because we timed out and the buffer is empty.
// Normally PowerShell generates this event, but now PowerShell assumes the engine is not idle because
// it called 'PSConsoleHostReadLine' which isn't returning. So we generate the event instead.
runPipelineForEventProcessing = true;
_singleton._engineIntrinsics.Events.GenerateEvent(PSEngineEvent.OnIdle, null, null, null);
_singleton._engineIntrinsics.Events.GenerateEvent(
PSEngineEvent.OnIdle,
sender: null,
args: null,
extraData: null);

// Break out so we don't genreate more than one 'OnIdle' event for a timeout.
break;
Expand All @@ -239,15 +244,36 @@ internal static PSKeyInfo ReadKey()
ps.AddScript("[System.Diagnostics.DebuggerHidden()]param() 0", useLocalScope: true);
}

// To detect output during possible event processing, see if the cursor moved
// and rerender if so.
var console = _singleton._console;
var y = console.CursorTop;
// To detect output during possible event processing, see if the cursor moved and rerender if so.
int cursorTop = _singleton._console.CursorTop;

// Start the pipeline to process events.
ps.Invoke();
if (y != console.CursorTop)

// Check if any event handler writes console output to the best of our effort, and adjust the initial coordinates in that case.
//
// I say "to the best of our effort" because the delegate handler for an event will mostly run on a background thread, and thus
// there is no guarantee about when the delegate would finish. So in an extreme case, there could be race conditions in console
// read/write: we are reading 'CursorTop' while the delegate is writing console output on a different thread.
// There is no much we can do about that extreme case. However, our focus here is the 'OnIdle' event, and its handler is usually
// a script block, which will run within the 'ps.Invoke()' call above.
//
// We detect new console output by checking if cursor top changed, but handle a very special case: an event handler changed our
// buffer, by calling 'Insert' for example.
// I know only checking on buffer length change doesn't cover the case where buffer changed but the length is the same. However,
// we mainly want to cover buffer changes made by an 'OnIdle' event handler, and we trigger 'OnIdle' event only if the buffer is
// empty. So, this check is efficient and good enough for that main scenario.
// When our buffer was changed by an event handler, we assume that was all the event handler did and there was no direct console
// output. So, we adjust the initial coordinates only if cursor top changed but there was no buffer change.
int newCursorTop = _singleton._console.CursorTop;
int newBufferLen = _singleton._buffer.Length;
if (cursorTop != newCursorTop && bufferLen == newBufferLen)
{
_singleton._initialY = console.CursorTop;
_singleton.Render();
_singleton._initialY = newCursorTop;
if (bufferLen > 0)
{
_singleton.Render();
}
}
}
}
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