From 8d5e993169256ed80cc208d010179e9ff3f55708 Mon Sep 17 00:00:00 2001
From: Michael Lotz <mmlr@mlotz.ch>
Date: Thu, 27 Aug 2009 02:15:20 +0000
Subject: [PATCH] mmlr+anevilyak: Unconditionally release the reader sem when
 the previous buffer size was 0 instead of testing for fParserWaiting as there
 is a race condition between setting it to true in the parser thread and
 checking for it in the reader thread so a release_sem() could be missed
 causing #4343. To reduce the possible side effect of needlessly looping
 through acquire_sem() for too many unconditionally released sems, we eat them
 in the parser thread once we're sure we can't miss an event because of that.
 Also added a TODO about a memcpy() optimization as pointed out by Rene.
 +alphabranch

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@32733 a95241bf-73f2-0310-859d-f6bbb57e9c96
---
 src/apps/terminal/TermParse.cpp | 14 ++++++++------
 src/apps/terminal/TermParse.h   |  1 -
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/apps/terminal/TermParse.cpp b/src/apps/terminal/TermParse.cpp
index 0f8d10607f..2e7c50e957 100644
--- a/src/apps/terminal/TermParse.cpp
+++ b/src/apps/terminal/TermParse.cpp
@@ -74,7 +74,6 @@ TermParse::TermParse(int fd)
 	fReadBufferSize(0),
 	fParserBufferSize(0),
 	fParserBufferOffset(0),
-	fParserWaiting(false),
 	fBuffer(NULL),
 	fQuitting(true)
 {
@@ -252,7 +251,7 @@ TermParse::PtyReader()
 			memcpy(fReadBuffer + readPos, buf, nread);
 
 		bufferSize = atomic_add(&fReadBufferSize, nread);
-		if (bufferSize == 0 && fParserWaiting)
+		if (bufferSize == 0)
 			release_sem(fReaderSem);
 
 		bufferSize += nread;
@@ -1012,16 +1011,17 @@ TermParse::_ReadParserBuffer()
 
 	// wait for new input from pty
 	if (fReadBufferSize == 0) {
-		fParserWaiting = true;
-
 		status_t status = B_OK;
 		while (fReadBufferSize == 0 && status == B_OK) {
 			do {
 				status = acquire_sem(fReaderSem);
 			} while (status == B_INTERRUPTED);
-		}
 
-		fParserWaiting = false;
+			// eat any sems that were released unconditionally
+			int32 semCount;
+			if (get_sem_count(fReaderSem, &semCount) == B_OK && semCount > 0)
+				acquire_sem_etc(fReaderSem, semCount, B_RELATIVE_TIMEOUT, 0);
+		}
 
 		if (status < B_OK) {
 			fBuffer->Lock();
@@ -1034,6 +1034,8 @@ TermParse::_ReadParserBuffer()
 		toRead = ESC_PARSER_BUFFER_SIZE;
 
 	for (int32 i = 0; i < toRead; i++) {
+		// TODO: This could be optimized using memcpy instead and
+		// calculating space left as in the PtyReader().
 		fParserBuffer[i] = fReadBuffer[fBufferPosition];
 		fBufferPosition = (fBufferPosition + 1) % READ_BUF_SIZE;
 	}
diff --git a/src/apps/terminal/TermParse.h b/src/apps/terminal/TermParse.h
index 4e881ff8d7..5b7fa84070 100644
--- a/src/apps/terminal/TermParse.h
+++ b/src/apps/terminal/TermParse.h
@@ -93,7 +93,6 @@ private:
 	uchar fParserBuffer[ESC_PARSER_BUFFER_SIZE];
 	int32 fParserBufferSize;
 	int32 fParserBufferOffset;
-	volatile bool fParserWaiting;
 	
 	int fLockFlag;