From 620bd2637b40d718dd5886ce7df0a19b73ea8875 Mon Sep 17 00:00:00 2001
From: Maksym Telychko <maksym.telychko@globallogic.com>
Date: Tue, 24 Mar 2020 17:41:04 +0200
Subject: MTX-3262 mpower: lockfile rewrite for interprocess communication
 safety

Previous implementation was not thread/interprocess safe due to pid
management
Fixes: Single instance guard.
---
 src/MTS_IO_LockFile.cpp | 92 ++++++++++++++-----------------------------------
 1 file changed, 25 insertions(+), 67 deletions(-)

(limited to 'src')

diff --git a/src/MTS_IO_LockFile.cpp b/src/MTS_IO_LockFile.cpp
index b74ba73..4312ce4 100644
--- a/src/MTS_IO_LockFile.cpp
+++ b/src/MTS_IO_LockFile.cpp
@@ -18,9 +18,9 @@
  *
  */
 
-/*! 
+/*!
  \file MTS_IO_LockFile.cpp
- \brief A brief description 
+ \brief A brief description
  \date Oct 8, 2014
  \author sgodinez
 
@@ -29,13 +29,7 @@
 
 #include <mts/MTS_IO_LockFile.h>
 #include <mts/MTS_Timer.h>
-#include <mts/MTS_Logger.h>
-#include <mts/MTS_System.h>
-#include <mts/MTS_Text.h>
 #include <sys/file.h>
-#include <sys/stat.h>
-#include <errno.h>
-#include <string.h>
 #include <unistd.h>
 
 using namespace MTS::IO;
@@ -43,79 +37,43 @@ using namespace MTS::IO;
 LockFile::LockFile(const std::string& sFile)
 : m_sFile(sFile)
 , m_iLockFd(-1)
+, m_iLockErr(-1)
 {
-
 }
 
-LockFile::~LockFile() {
+LockFile::~LockFile()
+{
     unlock();
 }
 
-bool LockFile::lock(uint32_t attemptMillis) {
-    if(isLocked()) {
+bool LockFile::lock(uint32_t attemptMillis)
+{
+    if (isLocked())
         return true;
-    }
 
     MTS::Timer timer;
-
     timer.start();
-    while(timer.getMillis() < attemptMillis) {
-        m_iLockFd =::open(m_sFile.c_str(), O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0644);
-        if (m_iLockFd < 0) {
-            // device already locked -> bail out
-            printWarning("LockFile| Failed to Lock [%s] [%d][%s]", m_sFile.c_str(), errno, strerror(errno));
-
-            //Check if lock file's process still exists
-            std::string sResult;
-            if(MTS::System::readFile(m_sFile, sResult) == 0 && sResult.size() > 0) {
-                struct stat sts;
-                std::string sProc = "/proc/" + MTS::Text::trim(sResult);
-                if (stat(sProc.c_str(), &sts) == -1 && errno == ENOENT) {
-                    printWarning("LockFile| Current Lock's Process [%s] does not exist.  Removing lock.", sResult.c_str());
-                    // process doesn't exist -> remove file
-                    ::unlink(m_sFile.c_str());
-                }
-            }
-
-        } else {
-            //TODO: Investigate using flock in addition to minicom-style lock : flock(m_iLockFd, LOCK_EX | LOCK_NB);
-
-            // %4d to make concurrent mgetty (if any) happy.
-            // Mgetty treats 4-bytes lock files as binary,
-            // not text, PID. Making 5+ char file. Brrr...
-            char buf[256] = {0};
-            size_t written = 0;
-
-            sprintf(buf, "%4d\n", getpid());
-            size_t wsize = strlen(buf);
-
-            written = write(m_iLockFd, buf, wsize);
-
-            if (wsize != written) {
-                printError("LockFile| Error writing to lock file [%s] [%d][%s]", m_sFile.c_str(), errno, strerror(errno));
-                close(m_iLockFd);
-                return false;
-            }
-            else {
-                close(m_iLockFd);
-                return true;
-            }
-        }
-        uint32_t randomSleepTime = ((rand() % 10) + 1) * 100000; //Sleep from 100ms to 1 Second
-        ::usleep(randomSleepTime);
+    m_iLockFd = ::open(m_sFile.c_str(), O_CREAT | O_RDWR, 0666);
+    while (timer.getMillis() < attemptMillis) {
+        m_iLockErr = ::flock(m_iLockFd, LOCK_EX | LOCK_NB);
+        if (m_iLockErr == 0)
+            return true;
+        ::usleep(((rand() % 10) + 1) * 100000); //Sleep from 100ms to 1 Second
     }
+    ::close(m_iLockFd);
+    m_iLockFd = -1;
     return false;
 }
 
-void LockFile::unlock() {
-    if(isLocked()) {
-        ::unlink(m_sFile.c_str());
-        //TODO: flock cleanup : flock(m_iLockFd, LOCK_UN);
-        m_iLockFd = -1;
-    }
+void LockFile::unlock()
+{
+    ::flock(m_iLockFd, LOCK_UN);
+    ::close(m_iLockFd);
+    m_iLockFd = -1;
+    m_iLockErr = -1;
 }
 
-bool LockFile::isLocked() {
-    return m_iLockFd >= 0;
+bool LockFile::isLocked()
+{
+    return m_iLockErr == 0;
 }
-
-- 
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