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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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22
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();
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);
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);
}
});
// 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.

35
src/libstore/build.cc
View File

@ -602,14 +602,7 @@ HookInstance::HookInstance()
builderOut.create();
/* Fork the hook. */
pid = fork();
switch (pid) {
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
pid = startProcess([&]() {
commonChildInit(fromHook);
@ -630,14 +623,8 @@ HookInstance::HookInstance()
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();
@ -2781,15 +2768,7 @@ void SubstitutionGoal::tryToRun()
const char * * argArr = strings2CharPtrs(args);
/* Fork the substitute program. */
pid = fork();
switch (pid) {
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
pid = startProcess([&]() {
commonChildInit(logPipe);
@ -2799,14 +2778,8 @@ void SubstitutionGoal::tryToRun()
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();

19
src/libstore/local-store.cc
View File

@ -1083,16 +1083,7 @@ 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();
run.pid = startProcess([&]() {
if (dup2(toPipe.readSide, STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (dup2(fromPipe.writeSide, STDOUT_FILENO) == -1)
@ -1101,13 +1092,7 @@ void LocalStore::startSubstituter(const Path & substituter, RunningSubstituter &
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.program = baseNameOf(substituter);
run.to = toPipe.writeSide.borrow();

77
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();
@ -801,25 +809,17 @@ 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) {
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
Pid pid = startProcess([&]() {
if (setuid(uid) == -1)
throw SysError("setting uid");
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;
#else
@ -830,14 +830,9 @@ void killUser(uid_t uid)
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);
}
_exit(0);
}
});
/* parent */
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();
@ -867,16 +881,7 @@ string runProgram(Path program, bool searchPath, const Strings & args)
pipe.create();
/* Fork. */
Pid pid;
pid = fork();
switch (pid) {
case -1:
throw SysError("unable to fork");
case 0: /* child */
try {
Pid pid = startProcess([&]() {
if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
@ -884,15 +889,9 @@ string runProgram(Path program, bool searchPath, const Strings & args)
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. */
});
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,

19
src/nix-daemon/nix-daemon.cc
View File

@ -872,17 +872,7 @@ 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();
switch (child) {
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
startProcess([&]() {
/* Background the daemon. */
if (setsid() == -1)
throw SysError(format("creating a new session"));
@ -901,11 +891,8 @@ static void daemonLoop()
to.fd = remote;
processConnection(trusted);
} catch (std::exception & e) {
writeToStderr("unexpected Nix daemon error: " + string(e.what()) + "\n");
}
exit(0);
}
_exit(0);
}, "unexpected Nix daemon error: ");
} catch (Interrupted & e) {
throw;

17
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 {
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);
} catch (std::exception & e) {
std::cerr << "error: " << e.what() << std::endl;
}
_exit(1);
}
});
fromDecompressor.writeSide.close();