From bf3cbafcdde36d3d3a8fabc7efe4645b40d6349e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Paul=20Mar=C3=A9chal?= <paul.marechal@ericsson.com>
Date: Wed, 24 Mar 2021 22:15:01 -0400
Subject: [PATCH] win: fix race condition when starting a watcher
MIME-Version: 1.0
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The `mRunner` thread sometimes runs after a delay, leading to a state
where `mRunning` is false and `pollDirectoryChanges` is called and does
nothing.

Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>
---
 includes/win32/Watcher.h |  1 +
 src/win32/Watcher.cpp    | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/includes/win32/Watcher.h b/includes/win32/Watcher.h
index ab63c8b0..5ddd9402 100644
--- a/includes/win32/Watcher.h
+++ b/includes/win32/Watcher.h
@@ -36,6 +36,7 @@ class Watcher
 
     std::atomic<bool> mRunning;
     SingleshotSemaphore mHasStartedSemaphore;
+    SingleshotSemaphore mIsRunningSemaphore;
     mutable std::mutex mErrorMutex;
     std::string mError;
 
diff --git a/src/win32/Watcher.cpp b/src/win32/Watcher.cpp
index 7483671a..9e4b8bac 100644
--- a/src/win32/Watcher.cpp
+++ b/src/win32/Watcher.cpp
@@ -38,7 +38,7 @@ std::string Watcher::getUTF8Directory(std::wstring path) {
     // before returning it to the user
     stripNTPrefix(uft16DirectoryString);
   }
-  
+
   int utf8length = WideCharToMultiByte(
       CP_UTF8,
       0,
@@ -239,6 +239,7 @@ void Watcher::start() {
   mRunner = std::thread([this] {
     // mRunning is set to false in the d'tor
     mRunning = true;
+    mIsRunningSemaphore.signal();
     run();
   });
 
@@ -247,11 +248,16 @@ void Watcher::start() {
     return;
   }
 
+  if (!mIsRunningSemaphore.waitFor(std::chrono::seconds(10))) {
+    setError("Watcher is not started");
+    return;
+  }
+
   QueueUserAPC([](__in ULONG_PTR self) {
     auto watcher = reinterpret_cast<Watcher*>(self);
     watcher->pollDirectoryChanges();
     watcher->mHasStartedSemaphore.signal();
-  } , mRunner.native_handle(), (ULONG_PTR)this);
+  }, mRunner.native_handle(), (ULONG_PTR)this);
 
   if (!mHasStartedSemaphore.waitFor(std::chrono::seconds(10))) {
     setError("Watcher is not started");