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[tests] Fix startup logcat race in MonitorAdbLogcat #12196

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Merged
jonathanpeppers merged 3 commits into from
Jul 21, 2026
Merged

[tests] Fix startup logcat race in MonitorAdbLogcat #12196

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ca7321e
Fix logcat startup race in device tests
jonathanpeppers Jul 21, 2026
89e416d
Trim follow-up diff for logcat flake fix
jonathanpeppers Jul 21, 2026
f150c74
Address PR review feedback in logcat matcher
jonathanpeppers Jul 21, 2026
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26 changes: 25 additions & 1 deletion src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/DeviceTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -369,11 +369,18 @@ protected static bool MonitorAdbLogcat (Func<string, bool> action, string logcat
bool didActionSucceed = false;
ManualResetEventSlim stdout_done = new ManualResetEventSlim ();
using (var sw = File.CreateText (logcatFilePath)) {
// Process already-buffered logcat lines first so startup messages emitted before
// this monitor starts are still visible to tests.
if (TryMatchLogcatOutput (RunAdbCommand ("logcat -d"), sw, action)) {
sw.Flush ();
return true;
}

using (var proc = Process.Start (info)) {
proc.OutputDataReceived += (sender, e) => {
if (e.Data != null) {
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sw.WriteLine (e.Data);
if (action (e.Data)) {
if (!didActionSucceed && action (e.Data)) {
didActionSucceed = true;
}
} else {
Expand All @@ -395,6 +402,23 @@ protected static bool MonitorAdbLogcat (Func<string, bool> action, string logcat
}
}

static bool TryMatchLogcatOutput (string output, TextWriter logcatOutput, Func<string, bool> action)
{
bool didActionSucceed = false;
using (var sr = new StringReader (output ?? "")) {
string line = sr.ReadLine ();
while (line != null) {
logcatOutput.WriteLine (line);
if (action (line)) {
didActionSucceed = true;
break;
}
line = sr.ReadLine ();
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}
}
return didActionSucceed;
}

protected static bool WaitForDebuggerToStart (string logcatFilePath, int timeout = 120)
{
bool result = MonitorAdbLogcat ((line) => {
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