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Refactoring: Move all fork handling into a higher-order function 

C++11 lambdas ftw.
This commit is contained in:
Eelco Dolstra 2014-07-10 16:50:51 +02:00
parent 1114c7bd57
commit 8e9140cfde
7 changed files with 128 additions and 206 deletions
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32
src/download-via-ssh/download-via-ssh.cc
View File

@ -24,30 +24,14 @@ static std::pair<FdSink, FdSource> connect(const string & conn)
Pipe to, from;
to.create();
from.create();
pid_t child = fork();
switch (child) {
case -1:
throw SysError("unable to fork");
case 0:
try {
restoreAffinity();
if (dup2(to.readSide, STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (dup2(from.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
execlp("ssh"
, "ssh"
, "-x"
, "-T"
, conn.c_str()
, "nix-store --serve"
, NULL);
throw SysError("executing ssh");
} catch (std::exception & e) {
std::cerr << "error: " << e.what() << std::endl;
}
_exit(1);
}
startProcess([&]() {
if (dup2(to.readSide, STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (dup2(from.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
execlp("ssh", "ssh", "-x", "-T", conn.c_str(), "nix-store --serve", NULL);
throw SysError("executing ssh");
});
// If child exits unexpectedly, we'll EPIPE or EOF early.
// If we exit unexpectedly, child will EPIPE or EOF early.
// So no need to keep track of it.

73
src/libstore/build.cc
View File

@ -602,42 +602,29 @@ HookInstance::HookInstance()
builderOut.create();
/* Fork the hook. */
pid = fork();
switch (pid) {
pid = startProcess([&]() {
case -1:
throw SysError("unable to fork");
commonChildInit(fromHook);
case 0:
try { /* child */
if (chdir("/") == -1) throw SysError("changing into `/");
commonChildInit(fromHook);
/* Dup the communication pipes. */
if (dup2(toHook.readSide, STDIN_FILENO) == -1)
throw SysError("dupping to-hook read side");
if (chdir("/") == -1) throw SysError("changing into `/");
/* Use fd 4 for the builder's stdout/stderr. */
if (dup2(builderOut.writeSide, 4) == -1)
throw SysError("dupping builder's stdout/stderr");
/* Dup the communication pipes. */
if (dup2(toHook.readSide, STDIN_FILENO) == -1)
throw SysError("dupping to-hook read side");
execl(buildHook.c_str(), buildHook.c_str(), settings.thisSystem.c_str(),
(format("%1%") % settings.maxSilentTime).str().c_str(),
(format("%1%") % settings.printBuildTrace).str().c_str(),
(format("%1%") % settings.buildTimeout).str().c_str(),
NULL);
/* Use fd 4 for the builder's stdout/stderr. */
if (dup2(builderOut.writeSide, 4) == -1)
throw SysError("dupping builder's stdout/stderr");
throw SysError(format("executing `%1%'") % buildHook);
});
execl(buildHook.c_str(), buildHook.c_str(), settings.thisSystem.c_str(),
(format("%1%") % settings.maxSilentTime).str().c_str(),
(format("%1%") % settings.printBuildTrace).str().c_str(),
(format("%1%") % settings.buildTimeout).str().c_str(),
NULL);
throw SysError(format("executing `%1%'") % buildHook);
} catch (std::exception & e) {
writeToStderr("build hook error: " + string(e.what()) + "\n");
}
_exit(1);
}
/* parent */
pid.setSeparatePG(true);
pid.setKillSignal(SIGTERM);
fromHook.writeSide.close();
@ -2781,32 +2768,18 @@ void SubstitutionGoal::tryToRun()
const char * * argArr = strings2CharPtrs(args);
/* Fork the substitute program. */
pid = fork();
pid = startProcess([&]() {
switch (pid) {
commonChildInit(logPipe);
case -1:
throw SysError("unable to fork");
if (dup2(outPipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("cannot dup output pipe into stdout");
case 0:
try { /* child */
execv(sub.c_str(), (char * *) argArr);
commonChildInit(logPipe);
throw SysError(format("executing `%1%'") % sub);
});
if (dup2(outPipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("cannot dup output pipe into stdout");
execv(sub.c_str(), (char * *) argArr);
throw SysError(format("executing `%1%'") % sub);
} catch (std::exception & e) {
writeToStderr("substitute error: " + string(e.what()) + "\n");
}
_exit(1);
}
/* parent */
pid.setSeparatePG(true);
pid.setKillSignal(SIGTERM);
outPipe.writeSide.close();

35
src/libstore/local-store.cc
View File

@ -1083,31 +1083,16 @@ void LocalStore::startSubstituter(const Path & substituter, RunningSubstituter &
setSubstituterEnv();
run.pid = fork();
switch (run.pid) {
case -1:
throw SysError("unable to fork");
case 0: /* child */
try {
restoreAffinity();
if (dup2(toPipe.readSide, STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (dup2(fromPipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
if (dup2(errorPipe.writeSide, STDERR_FILENO) == -1)
throw SysError("dupping stderr");
execl(substituter.c_str(), substituter.c_str(), "--query", NULL);
throw SysError(format("executing `%1%'") % substituter);
} catch (std::exception & e) {
std::cerr << "error: " << e.what() << std::endl;
}
_exit(1);
}
/* Parent. */
run.pid = startProcess([&]() {
if (dup2(toPipe.readSide, STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (dup2(fromPipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
if (dup2(errorPipe.writeSide, STDERR_FILENO) == -1)
throw SysError("dupping stderr");
execl(substituter.c_str(), substituter.c_str(), "--query", NULL);
throw SysError(format("executing `%1%'") % substituter);
});
run.program = baseNameOf(substituter);
run.to = toPipe.writeSide.borrow();

109
src/libutil/util.cc
View File

@ -1,5 +1,8 @@
#include "config.h"
#include "util.hh"
#include "affinity.hh"
#include <iostream>
#include <cerrno>
#include <cstdio>
@ -16,8 +19,6 @@
#include <sys/syscall.h>
#endif
#include "util.hh"
extern char * * environ;
@ -714,6 +715,13 @@ Pid::Pid()
}
Pid::Pid(pid_t pid)
{
Pid();
*this = pid;
}
Pid::~Pid()
{
kill();
@ -801,43 +809,30 @@ void killUser(uid_t uid)
users to which the current process can send signals. So we
fork a process, switch to uid, and send a mass kill. */
Pid pid;
pid = fork();
switch (pid) {
Pid pid = startProcess([&]() {
case -1:
throw SysError("unable to fork");
if (setuid(uid) == -1)
throw SysError("setting uid");
case 0:
try { /* child */
if (setuid(uid) == -1)
throw SysError("setting uid");
while (true) {
while (true) {
#ifdef __APPLE__
/* OSX's kill syscall takes a third parameter that, among other
things, determines if kill(-1, signo) affects the calling
process. In the OSX libc, it's set to true, which means
"follow POSIX", which we don't want here
/* OSX's kill syscall takes a third parameter that, among
other things, determines if kill(-1, signo) affects the
calling process. In the OSX libc, it's set to true,
which means "follow POSIX", which we don't want here
*/
if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
#else
if (kill(-1, SIGKILL) == 0) break;
if (kill(-1, SIGKILL) == 0) break;
#endif
if (errno == ESRCH) break; /* no more processes */
if (errno != EINTR)
throw SysError(format("cannot kill processes for uid `%1%'") % uid);
}
} catch (std::exception & e) {
writeToStderr((format("killing processes belonging to uid `%1%': %2%\n") % uid % e.what()).str());
_exit(1);
if (errno == ESRCH) break; /* no more processes */
if (errno != EINTR)
throw SysError(format("cannot kill processes for uid `%1%'") % uid);
}
_exit(0);
}
/* parent */
_exit(0);
});
int status = pid.wait(true);
if (status != 0)
throw Error(format("cannot kill processes for uid `%1%': %2%") % uid % statusToString(status));
@ -852,6 +847,25 @@ void killUser(uid_t uid)
//////////////////////////////////////////////////////////////////////
pid_t startProcess(std::function<void()> fun, const string & errorPrefix)
{
pid_t pid = fork();
if (pid == -1) throw SysError("unable to fork");
if (pid == 0) {
try {
restoreAffinity();
fun();
} catch (std::exception & e) {
writeToStderr(errorPrefix + string(e.what()) + "\n");
}
_exit(1);
}
return pid;
}
string runProgram(Path program, bool searchPath, const Strings & args)
{
checkInterrupt();
@ -867,32 +881,17 @@ string runProgram(Path program, bool searchPath, const Strings & args)
pipe.create();
/* Fork. */
Pid pid;
pid = fork();
Pid pid = startProcess([&]() {
if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
switch (pid) {
if (searchPath)
execvp(program.c_str(), (char * *) &cargs[0]);
else
execv(program.c_str(), (char * *) &cargs[0]);
case -1:
throw SysError("unable to fork");
case 0: /* child */
try {
if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
if (searchPath)
execvp(program.c_str(), (char * *) &cargs[0]);
else
execv(program.c_str(), (char * *) &cargs[0]);
throw SysError(format("executing `%1%'") % program);
} catch (std::exception & e) {
writeToStderr("error: " + string(e.what()) + "\n");
}
_exit(1);
}
/* Parent. */
throw SysError(format("executing `%1%'") % program);
});
pipe.writeSide.close();

7
src/libutil/util.hh
View File

@ -7,6 +7,7 @@
#include <dirent.h>
#include <unistd.h>
#include <signal.h>
#include <functional>
#include <cstdio>
@ -237,6 +238,7 @@ class Pid
int killSignal;
public:
Pid();
Pid(pid_t pid);
~Pid();
void operator =(pid_t pid);
operator pid_t();
@ -252,6 +254,11 @@ public:
void killUser(uid_t uid);
/* Fork a process that runs the given function, and return the child
pid to the caller. */
pid_t startProcess(std::function<void()> fun, const string & errorPrefix = "error: ");
/* Run a program and return its stdout in a string (i.e., like the
shell backtick operator). */
string runProgram(Path program, bool searchPath = false,

49
src/nix-daemon/nix-daemon.cc
View File

@ -872,40 +872,27 @@ static void daemonLoop()
printMsg(lvlInfo, format("accepted connection from pid %1%, uid %2%") % clientPid % clientUid);
/* Fork a child to handle the connection. */
pid_t child;
child = fork();
startProcess([&]() {
/* Background the daemon. */
if (setsid() == -1)
throw SysError(format("creating a new session"));
switch (child) {
/* Restore normal handling of SIGCHLD. */
setSigChldAction(false);
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
/* Background the daemon. */
if (setsid() == -1)
throw SysError(format("creating a new session"));
/* Restore normal handling of SIGCHLD. */
setSigChldAction(false);
/* For debugging, stuff the pid into argv[1]. */
if (clientPid != -1 && argvSaved[1]) {
string processName = int2String(clientPid);
strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
}
/* Handle the connection. */
from.fd = remote;
to.fd = remote;
processConnection(trusted);
} catch (std::exception & e) {
writeToStderr("unexpected Nix daemon error: " + string(e.what()) + "\n");
/* For debugging, stuff the pid into argv[1]. */
if (clientPid != -1 && argvSaved[1]) {
string processName = int2String(clientPid);
strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
}
exit(0);
}
/* Handle the connection. */
from.fd = remote;
to.fd = remote;
processConnection(trusted);
_exit(0);
}, "unexpected Nix daemon error: ");
} catch (Interrupted & e) {
throw;

29
src/nix-store/nix-store.cc
View File

@ -939,27 +939,14 @@ static void opServe(Strings opFlags, Strings opArgs)
Pipe fromDecompressor;
fromDecompressor.create();
Pid pid;
pid = fork();
switch (pid) {
case -1:
throw SysError("unable to fork");
case 0: /* child */
try {
fromDecompressor.readSide.close();
if (dup2(fromDecompressor.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
// FIXME: use absolute path.
execlp(compression.c_str(), compression.c_str(), "-d", NULL);
throw SysError(format("executing `%1%'") % compression);
} catch (std::exception & e) {
std::cerr << "error: " << e.what() << std::endl;
}
_exit(1);
}
Pid pid = startProcess([&]() {
fromDecompressor.readSide.close();
if (dup2(fromDecompressor.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
// FIXME: use absolute path.
execlp(compression.c_str(), compression.c_str(), "-d", NULL);
throw SysError(format("executing `%1%'") % compression);
});
fromDecompressor.writeSide.close();