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lint and style cleanups

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This commit is contained in:
Kurtis Rader 2017-08-06 15:47:01 -07:00
parent 083224d1c0
commit acdb81bbca
6 changed files with 89 additions and 86 deletions
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2
src/env.h
View file

@ -71,8 +71,8 @@ void misc_init();
class env_var_t {
private:
bool is_missing;
wcstring val;
bool is_missing;
public:
static env_var_t missing_var() {

82
src/exec.cpp
View file

@ -19,6 +19,7 @@
#include <unistd.h>
#include <algorithm>
#include <functional>
#include <map>
#include <memory>
#include <string>
@ -37,6 +38,7 @@
#include "postfork.h"
#include "proc.h"
#include "reader.h"
#include "signal.h"
#include "wutil.h" // IWYU pragma: keep
/// File descriptor redirection error message.
@ -493,8 +495,8 @@ void exec_job(parser_t &parser, job_t *j) {
// We are careful to set these to -1 when closed, so if we exit the loop abruptly, we can still
// close them.
bool pgrp_set = false;
//this is static since processes can block on input/output across jobs
//the main exec_job loop is only ever run in a single thread, so this is OK
// This is static since processes can block on input/output across jobs the main exec_job loop
// is only ever run in a single thread, so this is OK.
static pid_t blocked_pid = -1;
int pipe_current_read = -1, pipe_current_write = -1, pipe_next_read = -1;
for (std::unique_ptr<process_t> &unique_p : j->processes) {
@ -513,7 +515,7 @@ void exec_job(parser_t &parser, job_t *j) {
// See if we need a pipe.
const bool pipes_to_next_command = !p->is_last_in_job;
//set to true if we end up forking for this process
// Set to true if we end up forking for this process.
bool child_forked = false;
bool child_spawned = false;
bool block_child = true;
@ -622,12 +624,12 @@ void exec_job(parser_t &parser, job_t *j) {
// a pipeline.
shared_ptr<io_buffer_t> block_output_io_buffer;
//used to SIGCONT the previously SIGSTOP'd process so the main loop or next command in job can read
//from its output.
auto unblock_previous = [&j] () {
//we've already called waitpid after forking the child, so we've guaranteed that they're
//already SIGSTOP'd. Otherwise we'd be risking a deadlock because we can call SIGCONT before
//they've actually stopped, and they'll remain suspended indefinitely.
// Used to SIGCONT the previously SIGSTOP'd process so the main loop or next command in job
// can read from its output.
auto unblock_previous = [&j]() {
// We've already called waitpid after forking the child, so we've guaranteed that
// they're already SIGSTOP'd. Otherwise we'd be risking a deadlock because we can call
// SIGCONT before they've actually stopped, and they'll remain suspended indefinitely.
if (blocked_pid != -1) {
debug(2, L"Unblocking process %d.\n", blocked_pid);
kill(blocked_pid, SIGCONT);
@ -653,7 +655,7 @@ void exec_job(parser_t &parser, job_t *j) {
if (block_child) {
kill(p->pid, SIGSTOP);
}
//the parent will wake us up when we're ready to execute
// The parent will wake us up when we're ready to execute.
setup_child_process(p, process_net_io_chain);
child_action();
DIE("Child process returned control to do_fork lambda!");
@ -678,10 +680,9 @@ void exec_job(parser_t &parser, job_t *j) {
return true;
};
//helper routine executed by INTERNAL_FUNCTION and INTERNAL_BLOCK_NODE to make sure
//an output buffer exists in case there is another command in the job chain that will
//be reading from this command's output.
// Helper routine executed by INTERNAL_FUNCTION and INTERNAL_BLOCK_NODE to make sure an
// output buffer exists in case there is another command in the job chain that will be
// reading from this command's output.
auto verify_buffer_output = [&] () {
if (!p->is_last_in_job) {
// Be careful to handle failure, e.g. too many open fds.
@ -842,8 +843,8 @@ void exec_job(parser_t &parser, job_t *j) {
const int fg = j->get_flag(JOB_FOREGROUND);
j->set_flag(JOB_FOREGROUND, false);
//main loop may need to perform a blocking read from previous command's output.
//make sure read source is not blocked
// Main loop may need to perform a blocking read from previous command's output.
// Make sure read source is not blocked.
unblock_previous();
p->status = builtin_run(parser, p->get_argv(), *builtin_io_streams);
@ -939,8 +940,8 @@ void exec_job(parser_t &parser, job_t *j) {
bool must_fork = redirection_is_to_real_file(stdout_io.get()) ||
redirection_is_to_real_file(stderr_io.get());
if (!must_fork && p->is_last_in_job) {
//we are handling reads directly in the main loop. Make sure source is unblocked.
//Note that we may still end up forking.
// We are handling reads directly in the main loop. Make sure source is
// unblocked. Note that we may still end up forking.
unblock_previous();
const bool stdout_is_to_buffer = stdout_io && stdout_io->io_mode == IO_BUFFER;
const bool no_stdout_output = stdout_buffer.empty();
@ -1110,18 +1111,19 @@ void exec_job(parser_t &parser, job_t *j) {
bool child_blocked = block_child && child_forked;
if (child_blocked) {
//we have to wait to ensure the child has set their progress group and is in SIGSTOP state
//otherwise, we can later call SIGCONT before they call SIGSTOP and they'll be blocked indefinitely.
//The child is SIGSTOP'd and is guaranteed to have called child_set_group() at this point.
//but we only need to call set_child_group for the first process in the group.
//If needs_keepalive is set, this has already been called for the keepalive process
// We have to wait to ensure the child has set their progress group and is in SIGSTOP
// state otherwise, we can later call SIGCONT before they call SIGSTOP and they'll be
// blocked indefinitely. The child is SIGSTOP'd and is guaranteed to have called
// child_set_group() at this point. but we only need to call set_child_group for the
// first process in the group. If needs_keepalive is set, this has already been called
// for the keepalive process.
pid_t pid_status{};
int result;
while ((result = waitpid(p->pid, &pid_status, WUNTRACED)) == -1 && errno == EINTR) {
//This could be a superfluous interrupt or Ctrl+C at the terminal
//In all cases, it is OK to retry since the forking code above is specifically designed
//to never, ever hang/block in a child process before the SIGSTOP call is reached.
continue;
// This could be a superfluous interrupt or Ctrl+C at the terminal In all cases, it
// is OK to retry since the forking code above is specifically designed to never,
// ever hang/block in a child process before the SIGSTOP call is reached.
; // do nothing
}
if (result == -1) {
exec_error = true;
@ -1129,26 +1131,26 @@ void exec_job(parser_t &parser, job_t *j) {
wperror(L"waitpid");
break;
}
//we are not unblocking the child via SIGCONT just yet to give the next process a chance to open
//the pipes and join the process group. We only unblock the last process in the job chain because
//no one awaits it.
// We are not unblocking the child via SIGCONT just yet to give the next process a
// chance to open the pipes and join the process group. We only unblock the last process
// in the job chain because no one awaits it.
}
//regardless of whether the child blocked or not:
//only once per job, and only once we've actually executed an external command
// Regardless of whether the child blocked or not: only once per job, and only once we've
// actually executed an external command.
if ((child_spawned || child_forked) && !pgrp_set) {
//this should be called after waitpid if child_forked && pipes_to_next_command
//it can be called at any time if child_spawned
// This should be called after waitpid if child_forked and pipes_to_next_command it can
// be called at any time if child_spawned.
set_child_group(j, p->pid);
//we can't rely on p->is_first_in_job because a builtin may have been the first
// we can't rely on p->is_first_in_job because a builtin may have been the first.
pgrp_set = true;
}
//if the command we ran _before_ this one was SIGSTOP'd to let this one catch up, unblock it now.
//this must be after the wait_pid on the process we just started, if any.
// If the command we ran _before_ this one was SIGSTOP'd to let this one catch up, unblock
// it now. this must be after the wait_pid on the process we just started, if any.
unblock_previous();
if (child_blocked) {
//store the newly-blocked command's PID so that it can be SIGCONT'd once the next process
//in the chain is started. That may be in this job or in another job.
// Store the newly-blocked command's PID so that it can be SIGCONT'd once the next
// process in the chain is started. That may be in this job or in another job.
blocked_pid = p->pid;
}
@ -1164,7 +1166,7 @@ void exec_job(parser_t &parser, job_t *j) {
pipe_current_write = -1;
}
//unblock the last process because there's no need for it to stay SIGSTOP'd for anything
// Unblock the last process because there's no need for it to stay SIGSTOP'd for anything.
if (p->is_last_in_job) {
unblock_previous();
}

2
src/expand.h
View file

@ -122,8 +122,6 @@ bool expand_one(wcstring &inout_str, expand_flags_t flags, parse_error_list_t *e
/// Convert the variable value to a human readable form, i.e. escape things, handle arrays, etc.
/// Suitable for pretty-printing.
///
/// \param in the value to escape
wcstring expand_escape_variable(const env_var_t &var);
/// Perform tilde expansion and nothing else on the specified string, which is modified in place.

22
src/postfork.cpp
View file

@ -78,9 +78,9 @@ bool child_set_group(job_t *j, process_t *p) {
if (j->pgid == -2) {
j->pgid = p->pid;
}
//retry on EPERM because there's no way that a child cannot join an existing progress group
//because we are SIGSTOPing the previous job in the chain. Sometimes we have to try a few
//times to get the kernel to see the new group. (Linux 4.4.0)
// Retry on EPERM because there's no way that a child cannot join an existing progress group
// because we are SIGSTOPing the previous job in the chain. Sometimes we have to try a few
// times to get the kernel to see the new group. (Linux 4.4.0)
int failure = setpgid(p->pid, j->pgid);
while (failure == -1 && (errno == EPERM || errno == EINTR)) {
debug_safe(4, "Retrying setpgid in child process");
@ -112,7 +112,7 @@ bool child_set_group(job_t *j, process_t *p) {
retval = false;
}
} else {
//this is probably stays unused in the child
// This is probably stays unused in the child.
j->pgid = getpgrp();
}
@ -142,16 +142,16 @@ bool set_child_group(job_t *j, pid_t child_pid) {
if (j->get_flag(JOB_TERMINAL) && j->get_flag(JOB_FOREGROUND)) { //!OCLINT(early exit)
if (tcgetpgrp(STDIN_FILENO) == j->pgid) {
//we've already assigned the process group control of the terminal when the first process in the job
//was started. There's no need to do so again, and on some platforms this can cause an EPERM error.
//In addition, if we've given control of the terminal to a process group, attempting to call tcsetpgrp
//from the background will cause SIGTTOU to be sent to everything in our process group (unless we
//handle it)..
// We've already assigned the process group control of the terminal when the first
// process in the job was started. There's no need to do so again, and on some platforms
// this can cause an EPERM error. In addition, if we've given control of the terminal to
// a process group, attempting to call tcsetpgrp from the background will cause SIGTTOU
// to be sent to everything in our process group (unless we handle it).
debug(4, L"Process group %d already has control of terminal\n", j->pgid);
}
else
{
//no need to duplicate the code here, a function already exists that does just this
// No need to duplicate the code here, a function already exists that does just this.
retval = terminal_give_to_job(j, false /*new job, so not continuing*/);
}
}
@ -264,7 +264,7 @@ int setup_child_process(process_t *p, const io_chain_t &io_chain) {
bool ok = true;
if (ok) {
//In the case of IO_FILE, this can hang until data is available to read/write!
// In the case of IO_FILE, this can hang until data is available to read/write!
ok = (0 == handle_child_io(io_chain));
if (p != 0 && !ok) {
debug_safe(4, "handle_child_io failed in setup_child_process");

1
src/postfork.h
View file

@ -27,7 +27,6 @@ bool child_set_group(job_t *j, process_t *p); //called by child
/// inside the exec function, which blocks all signals), and all IO redirections and other file
/// descriptor actions are performed.
///
/// \param j the job to set up the IO for
/// \param p the child process to set up
/// \param io_chain the IO chain to use
///

66
src/proc.cpp
View file

@ -791,53 +791,56 @@ bool terminal_give_to_job(job_t *j, int cont) {
signal_block();
//It may not be safe to call tcsetpgrp if we've already done so, as at that point we are no longer
//the controlling process group for the terminal and no longer have permission to set the process
//group that is in control, causing tcsetpgrp to return EPERM, even though that's not the documented
//behavior in tcsetpgrp(3), which instead says other bad things will happen (it says SIGTTOU will be
//sent to all members of the background *calling* process group, but it's more complicated than that,
//SIGTTOU may or may not be sent depending on the TTY configuration and whether or not signal handlers
//for SIGTTOU are installed. Read: http://curiousthing.org/sigttin-sigttou-deep-dive-linux
//In all cases, our goal here was just to hand over control of the terminal to this process group,
//which is a no-op if it's already been done.
// It may not be safe to call tcsetpgrp if we've already done so, as at that point we are no
// longer the controlling process group for the terminal and no longer have permission to set
// the process group that is in control, causing tcsetpgrp to return EPERM, even though that's
// not the documented behavior in tcsetpgrp(3), which instead says other bad things will happen
// (it says SIGTTOU will be sent to all members of the background *calling* process group, but
// it's more complicated than that, SIGTTOU may or may not be sent depending on the TTY
// configuration and whether or not signal handlers for SIGTTOU are installed. Read:
// http://curiousthing.org/sigttin-sigttou-deep-dive-linux In all cases, our goal here was just
// to hand over control of the terminal to this process group, which is a no-op if it's already
// been done.
if (tcgetpgrp(STDIN_FILENO) == j->pgid) {
debug(2, L"Process group %d already has control of terminal\n", j->pgid);
}
else {
debug(4, L"Attempting to bring process group to foreground via tcsetpgrp for job->pgid %d\n", j->pgid);
//the tcsetpgrp(2) man page says that EPERM is thrown if "pgrp has a supported value, but is not the
//process group ID of a process in the same session as the calling process."
//Since we _guarantee_ that this isn't the case (the child calls setpgid before it calls SIGSTOP, and
//the child was created in the same session as us), it seems that EPERM is being thrown because of an
//caching issue - the call to tcsetpgrp isn't seeing the newly-created process group just yet. On this
//developer's test machine (WSL running Linux 4.4.0), EPERM does indeed disappear on retry. The important
//thing is that we can guarantee the process isn't going to exit while we wait (which would cause us to
//possibly block indefinitely).
// The tcsetpgrp(2) man page says that EPERM is thrown if "pgrp has a supported value, but
// is not the process group ID of a process in the same session as the calling process."
// Since we _guarantee_ that this isn't the case (the child calls setpgid before it calls
// SIGSTOP, and the child was created in the same session as us), it seems that EPERM is
// being thrown because of an caching issue - the call to tcsetpgrp isn't seeing the
// newly-created process group just yet. On this developer's test machine (WSL running Linux
// 4.4.0), EPERM does indeed disappear on retry. The important thing is that we can
// guarantee the process isn't going to exit while we wait (which would cause us to possibly
// block indefinitely).
while (tcsetpgrp(STDIN_FILENO, j->pgid) != 0) {
bool pgroup_terminated = false;
if (errno == EINTR) {
//always retry on EINTR, see comments in tcsetattr EINTR code below.
; // Always retry on EINTR, see comments in tcsetattr EINTR code below.
}
else if (errno == EINVAL) {
//OS X returns EINVAL if the process group no longer lives. Probably other OSes, too.
//Unlike EPERM below, EINVAL can only happen if the process group has terminated
// OS X returns EINVAL if the process group no longer lives. Probably other OSes,
// too. Unlike EPERM below, EINVAL can only happen if the process group has
// terminated.
pgroup_terminated = true;
}
else if (errno == EPERM) {
//retry so long as this isn't because the process group is dead
// Retry so long as this isn't because the process group is dead.
int wait_result = waitpid(-1 * j->pgid, &wait_result, WNOHANG);
if (wait_result == -1) {
//Note that -1 is technically an "error" for waitpid in the sense that an invalid argument was specified
//because no such process group exists any longer. This is the observed behavior on Linux 4.4.0.
//a "success" result would mean processes from the group still exist but is still running in some state
//or the other.
// Note that -1 is technically an "error" for waitpid in the sense that an
// invalid argument was specified because no such process group exists any
// longer. This is the observed behavior on Linux 4.4.0. a "success" result
// would mean processes from the group still exist but is still running in some
// state or the other.
pgroup_terminated = true;
}
else {
//debug the original tcsetpgrp error (not the waitpid errno) to the log, and then retry until not EPERM
//or the process group has exited.
// Debug the original tcsetpgrp error (not the waitpid errno) to the log, and
// then retry until not EPERM or the process group has exited.
debug(2, L"terminal_give_to_job(): EPERM.\n", j->pgid);
}
}
@ -850,9 +853,10 @@ bool terminal_give_to_job(job_t *j, int cont) {
}
if (pgroup_terminated) {
//all processes in the process group has exited. Since we force all child procs to SIGSTOP on startup,
//the only way that can happen is if the very last process in the group terminated, and didn't need
//to access the terminal, otherwise it would have hung waiting for terminal IO (SIGTTIN). We can ignore this.
// All processes in the process group has exited. Since we force all child procs to
// SIGSTOP on startup, the only way that can happen is if the very last process in
// the group terminated, and didn't need to access the terminal, otherwise it would
// have hung waiting for terminal IO (SIGTTIN). We can ignore this.
debug(3, L"tcsetpgrp called but process group %d has terminated.\n", j->pgid);
break;
}