1 /*
2  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #include "modules/desktop_capture/screen_drawer_lock_posix.h"
12 
13 #include <fcntl.h>
14 #include <sys/stat.h>
15 
16 #include "rtc_base/checks.h"
17 #include "rtc_base/logging.h"
18 
19 namespace webrtc {
20 
21 namespace {
22 
23 // A uuid as the name of semaphore.
24 static constexpr char kSemaphoreName[] = "GSDL54fe5552804711e6a7253f429a";
25 
26 }  // namespace
27 
ScreenDrawerLockPosix()28 ScreenDrawerLockPosix::ScreenDrawerLockPosix()
29     : ScreenDrawerLockPosix(kSemaphoreName) {}
30 
ScreenDrawerLockPosix(const char * name)31 ScreenDrawerLockPosix::ScreenDrawerLockPosix(const char* name) {
32   semaphore_ = sem_open(name, O_CREAT, S_IRWXU | S_IRWXG | S_IRWXO, 1);
33   if (semaphore_ == SEM_FAILED) {
34     RTC_LOG_ERRNO(LS_ERROR) << "Failed to create named semaphore with " << name;
35     RTC_NOTREACHED();
36   }
37 
38   sem_wait(semaphore_);
39 }
40 
~ScreenDrawerLockPosix()41 ScreenDrawerLockPosix::~ScreenDrawerLockPosix() {
42   if (semaphore_ == SEM_FAILED) {
43     return;
44   }
45 
46   sem_post(semaphore_);
47   sem_close(semaphore_);
48   // sem_unlink a named semaphore won't wait until other clients to release the
49   // sem_t. So if a new process starts, it will sem_open a different kernel
50   // object with the same name and eventually breaks the cross-process lock.
51 }
52 
53 // static
Unlink(const char * name)54 void ScreenDrawerLockPosix::Unlink(const char* name) {
55   sem_unlink(name);
56 }
57 
58 }  // namespace webrtc
59