single-instance: latter instances will ask the legal instance to show itself

src/main.cpp

@@ -136,6 +136,8 @@ int main(int argc, char *argv[])
         // Ask another instance to open files passed in.
         if (!filePaths.isEmpty()) {
             guard.openExternalFiles(filePaths);
+        } else {
+            guard.showInstance();
         }
 
         return 0;

src/vmainwindow.cpp

@@ -1906,6 +1906,12 @@ void VMainWindow::checkSharedMemory()
         qDebug() << "shared memory fetch files" << files;
         openExternalFiles(files);
 
+        // Eliminate the signal.
+        m_guard->fetchAskedToShow();
+
+        showMainWindow();
+    } else if (m_guard->fetchAskedToShow()) {
+        qDebug() << "shared memory asked to show up";
         showMainWindow();
     }
 }

src/vsingleinstanceguard.cpp

@@ -29,6 +29,7 @@ bool VSingleInstanceGuard::tryRun()
         SharedStruct *str = (SharedStruct *)m_sharedMemory.data();
         str->m_magic = c_magic;
         str->m_filesBufIdx = 0;
+        str->m_askedToShow = false;
         m_sharedMemory.unlock();
         return true;
     } else {
@@ -130,3 +131,37 @@ QStringList VSingleInstanceGuard::fetchFilesToOpen()
 
     return files;
 }
+
+void VSingleInstanceGuard::showInstance()
+{
+    if (!m_sharedMemory.isAttached()) {
+        if (!m_sharedMemory.attach()) {
+            qDebug() << "fail to attach to the shared memory segment"
+                     << (m_sharedMemory.error() ? m_sharedMemory.errorString() : "");
+            return;
+        }
+    }
+
+    m_sharedMemory.lock();
+    SharedStruct *str = (SharedStruct *)m_sharedMemory.data();
+    V_ASSERT(str->m_magic == c_magic);
+    str->m_askedToShow = true;
+    m_sharedMemory.unlock();
+
+    qDebug() << "try to request another instance to show up";
+}
+
+bool VSingleInstanceGuard::fetchAskedToShow()
+{
+    bool ret = false;
+
+    Q_ASSERT(m_sharedMemory.isAttached());
+    m_sharedMemory.lock();
+    SharedStruct *str = (SharedStruct *)m_sharedMemory.data();
+    Q_ASSERT(str->m_magic == c_magic);
+    ret = str->m_askedToShow;
+    str->m_askedToShow = false;
+    m_sharedMemory.unlock();
+
+    return ret;
+}

src/vsingleinstanceguard.h

@@ -18,10 +18,16 @@ public:
     // via command line arguments.
     void openExternalFiles(const QStringList &p_files);
 
+    // Ask another instance to show itself.
+    void showInstance();
+
     // Fetch files from shared memory to open.
     // Will clear the shared memory.
     QStringList fetchFilesToOpen();
 
+    // Whether this instance is asked to show itself.
+    bool fetchAskedToShow();
+
 private:
     // The count of the entries in the buffer to hold the path of the files to open.
     enum { FilesBufCount = 1024 };
@@ -38,6 +44,9 @@ private:
         // [size of file1][file1][size of file2][file 2]
         // Unicode representation of QString.
         ushort m_filesBuf[FilesBufCount];
+
+        // Whether other instances ask to show the legal instance.
+        bool m_askedToShow;
     };
 
     // Append @p_file to the shared struct files buffer.