Test iortrans-4.8.2 demos an infinite loop. Possible trouble with

pushback buffers.

2 files changed, 25 insertions, 0 deletions

diff --git a/generic/tclIO.c b/generic/tclIO.c
index e6439ef..41ac1e1 100644
--- a/generic/tclIO.c
+++ b/generic/tclIO.c
@@ -5611,6 +5611,11 @@ DoReadChars(
 		ResetFlag(statePtr, CHANNEL_BLOCKED);
 	    }
 	    result = GetInput(chanPtr);
+if (chanPtr != statePtr->topChanPtr) {
+Tcl_Release(chanPtr);
+chanPtr = statePtr->topChanPtr;
+Tcl_Preserve(chanPtr);
+}
 	    if (result != 0) {
 		if (result == EAGAIN) {
 		    break;
diff --git a/tests/ioTrans.test b/tests/ioTrans.test
index b21d894..3bbd170 100644
--- a/tests/ioTrans.test
+++ b/tests/ioTrans.test
@@ -559,6 +559,26 @@ test iortrans-4.8.1 {chan read, bug 721ec69271} -setup {
     rename foo {}
 } -result {{read rt* {test data
 }} file*}
+test iortrans-4.8.2 {chan read, bug 721ec69271} -setup {
+    set res {}
+} -match glob -body {
+    proc foo {fd args} {
+	handle.initialize
+	handle.finalize
+	lappend ::res $args
+	# Kill and recreate transform while it is operating
+	chan pop $fd
+	chan push $fd [list foo $fd]
+	return x
+    }
+    set c [chan push [set c [tempchan]] [list foo $c]]
+    chan configure $c -buffersize 1
+    lappend res [read $c]
+} -cleanup {
+    tempdone
+    rename foo {}
+} -result {{read rt* {test data
+}} file*}
 test iortrans-4.9 {chan read, gets, bug 2921116} -setup {
     set res {}
 } -match glob -body {