diff options
Diffstat (limited to 'chromium/sandbox/linux/services/thread_helpers.cc')
-rw-r--r-- | chromium/sandbox/linux/services/thread_helpers.cc | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/chromium/sandbox/linux/services/thread_helpers.cc b/chromium/sandbox/linux/services/thread_helpers.cc new file mode 100644 index 00000000000..e0794f84a44 --- /dev/null +++ b/chromium/sandbox/linux/services/thread_helpers.cc @@ -0,0 +1,84 @@ +// Copyright 2014 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#include "sandbox/linux/services/thread_helpers.h" + +#include <errno.h> +#include <signal.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <unistd.h> + +#include <string> + +#include "base/basictypes.h" +#include "base/logging.h" +#include "base/posix/eintr_wrapper.h" +#include "base/strings/string_number_conversions.h" +#include "base/threading/platform_thread.h" +#include "base/threading/thread.h" + +namespace sandbox { + +bool ThreadHelpers::IsSingleThreaded(int proc_self_task) { + CHECK_LE(0, proc_self_task); + struct stat task_stat; + int fstat_ret = fstat(proc_self_task, &task_stat); + PCHECK(0 == fstat_ret); + + // At least "..", "." and the current thread should be present. + CHECK_LE(3UL, task_stat.st_nlink); + // Counting threads via /proc/self/task could be racy. For the purpose of + // determining if the current proces is monothreaded it works: if at any + // time it becomes monothreaded, it'll stay so. + return task_stat.st_nlink == 3; +} + +bool ThreadHelpers::StopThreadAndWatchProcFS(int proc_self_task, + base::Thread* thread) { + DCHECK_LE(0, proc_self_task); + DCHECK(thread); + const base::PlatformThreadId thread_id = thread->thread_id(); + const std::string thread_id_dir_str = base::IntToString(thread_id) + "/"; + + // The kernel is at liberty to wake the thread id futex before updating + // /proc. Following Stop(), the thread is joined, but entries in /proc may + // not have been updated. + thread->Stop(); + + unsigned int iterations = 0; + bool thread_present_in_procfs = true; + // Poll /proc with an exponential back-off, sleeping 2^iterations nanoseconds + // in nanosleep(2). + // Note: the clock may not allow for nanosecond granularity, in this case the + // first iterations would sleep a tiny bit more instead, which would not + // change the calculations significantly. + while (thread_present_in_procfs) { + struct stat task_stat; + const int fstat_ret = + fstatat(proc_self_task, thread_id_dir_str.c_str(), &task_stat, 0); + if (fstat_ret < 0) { + PCHECK(ENOENT == errno); + // The thread disappeared from /proc, we're done. + thread_present_in_procfs = false; + break; + } + // Increase the waiting time exponentially. + struct timespec ts = {0, 1L << iterations /* nanoseconds */}; + PCHECK(0 == HANDLE_EINTR(nanosleep(&ts, &ts))); + ++iterations; + + // Crash after 30 iterations, which means having spent roughly 2s in + // nanosleep(2) cumulatively. + CHECK_GT(30U, iterations); + // In practice, this never goes through more than a couple iterations. In + // debug mode, crash after 64ms (+ eventually 25 times the granularity of + // the clock) in nanosleep(2). + DCHECK_GT(25U, iterations); + } + + return true; +} + +} // namespace sandbox |