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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include <errno.h>
      6 #include <fcntl.h>
      7 #include <sys/file.h>
      8 
      9 #include "chrome/browser/process_singleton.h"
     10 
     11 #include "base/metrics/histogram.h"
     12 #include "base/posix/eintr_wrapper.h"
     13 #include "chrome/common/chrome_constants.h"
     14 
     15 namespace {
     16 
     17 // From "man 2 intro", the largest errno is |EOPNOTSUPP|, which is
     18 // |102|.  Since the histogram memory usage is proportional to this
     19 // number, using the |102| directly rather than the macro.
     20 const int kMaxErrno = 102;
     21 
     22 }  // namespace
     23 
     24 // This class is used to funnel messages to a single instance of the browser
     25 // process. This is needed for several reasons on other platforms.
     26 //
     27 // On Windows, when the user re-opens the application from the shell (e.g. an
     28 // explicit double-click, a shortcut that opens a webpage, etc.) we need to send
     29 // the message to the currently-existing copy of the browser.
     30 //
     31 // On Linux, opening a URL is done by creating an instance of the web browser
     32 // process and passing it the URL to go to on its commandline.
     33 //
     34 // Neither of those cases apply on the Mac. Launch Services ensures that there
     35 // is only one instance of the process, and we get URLs to open via AppleEvents
     36 // and, once again, the Launch Services system. We have no need to manage this
     37 // ourselves.  An exclusive lock is used to flush out anyone making incorrect
     38 // assumptions.
     39 
     40 ProcessSingleton::ProcessSingleton(
     41     const base::FilePath& user_data_dir,
     42     const NotificationCallback& /* notification_callback */)
     43     : lock_path_(user_data_dir.Append(chrome::kSingletonLockFilename)),
     44       lock_fd_(-1) {
     45 }
     46 
     47 ProcessSingleton::~ProcessSingleton() {
     48   // Make sure the lock is released.  Process death will also release
     49   // it, even if this is not called.
     50   Cleanup();
     51 }
     52 
     53 ProcessSingleton::NotifyResult ProcessSingleton::NotifyOtherProcess() {
     54   // This space intentionally left blank.
     55   return PROCESS_NONE;
     56 }
     57 
     58 ProcessSingleton::NotifyResult ProcessSingleton::NotifyOtherProcessOrCreate() {
     59   // Windows tries NotifyOtherProcess() first.
     60   return Create() ? PROCESS_NONE : PROFILE_IN_USE;
     61 }
     62 
     63 // Attempt to acquire an exclusive lock on an empty file in the
     64 // profile directory.  Returns |true| if it gets the lock.  Returns
     65 // |false| if the lock is held, or if there is an error.
     66 // |notification_callback| is not actually used. See the comments at the top of
     67 // this file for details.
     68 // TODO(shess): Rather than logging failures, popup an alert.  Punting
     69 // that for now because it would require confidence that this code is
     70 // never called in a situation where an alert wouldn't work.
     71 // http://crbug.com/59061
     72 bool ProcessSingleton::Create() {
     73   DCHECK_EQ(-1, lock_fd_) << "lock_path_ is already open.";
     74 
     75   lock_fd_ = HANDLE_EINTR(open(lock_path_.value().c_str(),
     76                                O_RDONLY | O_CREAT, 0644));
     77   if (lock_fd_ == -1) {
     78     const int capture_errno = errno;
     79     DPCHECK(lock_fd_ != -1) << "Unexpected failure opening profile lockfile";
     80     UMA_HISTOGRAM_ENUMERATION("ProcessSingleton.OpenError",
     81                               capture_errno, kMaxErrno);
     82     return false;
     83   }
     84 
     85   // Acquire an exclusive lock in non-blocking fashion.  If the lock
     86   // is already held, this will return |EWOULDBLOCK|.
     87   int rc = HANDLE_EINTR(flock(lock_fd_, LOCK_EX|LOCK_NB));
     88   if (rc == -1) {
     89     const int capture_errno = errno;
     90     DPCHECK(errno == EWOULDBLOCK)
     91         << "Unexpected failure locking profile lockfile";
     92 
     93     Cleanup();
     94 
     95     // Other errors indicate something crazy is happening.
     96     if (capture_errno != EWOULDBLOCK) {
     97       UMA_HISTOGRAM_ENUMERATION("ProcessSingleton.LockError",
     98                                 capture_errno, kMaxErrno);
     99       return false;
    100     }
    101 
    102     // The file is open by another process and locked.
    103     LOG(ERROR) << "Unable to obtain profile lock.";
    104     return false;
    105   }
    106 
    107   return true;
    108 }
    109 
    110 void ProcessSingleton::Cleanup() {
    111   // Closing the file also releases the lock.
    112   if (lock_fd_ != -1) {
    113     int rc = IGNORE_EINTR(close(lock_fd_));
    114     DPCHECK(!rc) << "Closing lock_fd_:";
    115   }
    116   lock_fd_ = -1;
    117 }
    118