* Catch SIGINT to terminate cleanly when the user tries to interrupt

Nix.  This is to prevent Berkeley DB from becoming wedged.

  Unfortunately it is not possible to throw C++ exceptions from a
  signal handler.  In fact, you can't do much of anything except
  change variables of type `volatile sig_atomic_t'.  So we set an
  interrupt flag in the signal handler and check it at various
  strategic locations in the code (by calling checkInterrupt()).
  Since this is unlikely to cover all cases (e.g., (semi-)infinite
  loops), sometimes SIGTERM may now be required to kill Nix.

src/libexpr/eval.cc

@@ -227,6 +227,8 @@ Expr evalExpr2(EvalState & state, Expr e)
 
 Expr evalExpr(EvalState & state, Expr e)
 {
+    checkInterrupt();
+    
     startNest(nest, lvlVomit,
         format("evaluating expression: %1%") % e);
 

src/libexpr/nixexpr.cc

@@ -87,6 +87,8 @@ string aterm2String(ATerm t)
 
 ATerm bottomupRewrite(TermFun & f, ATerm e)
 {
+    checkInterrupt();
+
     if (ATgetType(e) == AT_APPL) {
         AFun fun = ATgetAFun(e);
         int arity = ATgetArity(fun);
@@ -149,6 +151,8 @@ Expr makeAttrs(const ATermMap & attrs)
 
 Expr substitute(const ATermMap & subs, Expr e)
 {
+    checkInterrupt();
+
     ATMatcher m;
     string s;
 

src/libexpr/parser.cc

@@ -26,6 +26,8 @@ struct Cleanup : TermFun
 
     virtual ATerm operator () (ATerm e)
     {
+        checkInterrupt();
+        
         ATMatcher m;
         string s;
 

src/libmain/shared.cc

@@ -12,6 +12,12 @@ extern "C" {
 #include "config.h"
 
 
+void sigintHandler(int signo)
+{
+    _isInterrupted = 1;
+}
+
+
 /* Initialize and reorder arguments, then call the actual argument
    processor. */
 static void initAndRun(int argc, char * * argv)
@@ -23,6 +29,15 @@ static void initAndRun(int argc, char * * argv)
     nixStateDir = (string) NIX_STATE_DIR;
     nixDBPath = (string) NIX_STATE_DIR + "/db";
 
+    /* Catch SIGINT. */
+    struct sigaction act, oact;
+    act.sa_handler = sigintHandler;
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(SIGINT, &act, &oact))
+        throw SysError("installing handler for SIGINT");
+    printMsg(lvlError, "SIG HANDLER INSTALLED");
+
     /* Put the arguments in a vector. */
     Strings args, remaining;
     while (argc--) args.push_back(*argv++);

src/libstore/db.cc

@@ -80,6 +80,7 @@ void Transaction::moveTo(Transaction & t)
 
 void Database::requireEnv()
 {
+    checkInterrupt();
     if (!env) throw Error("database environment not open");
 }
 
@@ -310,6 +311,8 @@ TableId Database::openTable(const string & tableName)
 bool Database::queryString(const Transaction & txn, TableId table, 
     const string & key, string & data)
 {
+    checkInterrupt();
+
     try {
         Db * db = getDb(table);
 
@@ -367,6 +370,7 @@ bool Database::queryStrings(const Transaction & txn, TableId table,
 void Database::setString(const Transaction & txn, TableId table,
     const string & key, const string & data)
 {
+    checkInterrupt();
     try {
         Db * db = getDb(table);
         Dbt kt((void *) key.c_str(), key.length());
@@ -402,6 +406,7 @@ void Database::setStrings(const Transaction & txn, TableId table,
 void Database::delPair(const Transaction & txn, TableId table,
     const string & key)
 {
+    checkInterrupt();
     try {
         Db * db = getDb(table);
         Dbt kt((void *) key.c_str(), key.length());
@@ -423,9 +428,11 @@ void Database::enumTable(const Transaction & txn, TableId table,
         DestroyDbc destroyDbc(dbc);
 
         Dbt kt, dt;
-        while (dbc->get(&kt, &dt, DB_NEXT) != DB_NOTFOUND)
+        while (dbc->get(&kt, &dt, DB_NEXT) != DB_NOTFOUND) {
+            checkInterrupt();
             keys.push_back(
                 string((char *) kt.get_data(), kt.get_size()));
+        }
 
     } catch (DbException e) { rethrow(e); }
 }

src/libstore/exec.cc

@@ -109,6 +109,8 @@ void runProgram(const string & program,
     if (waitpid(pid, &status, 0) != pid)
         throw Error("unable to wait for child");
 
+    checkInterrupt();
+
     if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 	if (keepFailed) {
 	    printMsg(lvlTalkative, 

src/libstore/normalise.cc

@@ -96,6 +96,7 @@ Path normaliseStoreExpr(const Path & _nePath, PathSet pending)
     for (PathSet::iterator i = ne.derivation.inputs.begin();
          i != ne.derivation.inputs.end(); i++)
     {
+        checkInterrupt();
         Path nfPath = normaliseStoreExpr(*i, pending);
         realiseClosure(nfPath, pending);
         /* !!! nfPath should be a root of the garbage collector while
@@ -193,6 +194,7 @@ Path normaliseStoreExpr(const Path & _nePath, PathSet pending)
         for (Paths::iterator j = refPaths.begin();
 	     j != refPaths.end(); j++)
 	{
+            checkInterrupt();
 	    Path path = *j;
 	    elem.refs.insert(path);
             if (inClosures.find(path) != inClosures.end())
@@ -209,6 +211,7 @@ Path normaliseStoreExpr(const Path & _nePath, PathSet pending)
     PathSet donePaths;
 
     while (!usedPaths.empty()) {
+        checkInterrupt();
 	PathSet::iterator i = usedPaths.begin();
 	Path path = *i;
 	usedPaths.erase(i);
@@ -291,6 +294,7 @@ void ensurePath(const Path & path, PathSet pending)
     for (Paths::iterator i = subPaths.begin(); 
          i != subPaths.end(); i++)
     {
+        checkInterrupt();
         try {
             normaliseStoreExpr(*i, pending);
             if (isValidPath(path)) return;
@@ -337,6 +341,8 @@ static void requisitesWorker(const Path & nePath,
     bool includeExprs, bool includeSuccessors,
     PathSet & paths, PathSet & doneSet)
 {
+    checkInterrupt();
+    
     if (doneSet.find(nePath) != doneSet.end()) return;
     doneSet.insert(nePath);
 

src/libstore/pathlocks.cc

@@ -19,11 +19,14 @@ bool lockFile(int fd, LockType lockType, bool wait)
     lock.l_len = 0; /* entire file */
 
     if (wait) {
-        while (fcntl(fd, F_SETLKW, &lock) != 0)
+        while (fcntl(fd, F_SETLKW, &lock) != 0) {
+            checkInterrupt();
             if (errno != EINTR)
                 throw SysError(format("acquiring/releasing lock"));
+        }
     } else {
         while (fcntl(fd, F_SETLK, &lock) != 0) {
+            checkInterrupt();
             if (errno == EACCES || errno == EAGAIN) return false;
             if (errno != EINTR) 
                 throw SysError(format("acquiring/releasing lock"));
@@ -55,6 +58,7 @@ PathLocks::PathLocks(const PathSet & _paths)
     
     /* Acquire the lock for each path. */
     for (Paths::iterator i = paths.begin(); i != paths.end(); i++) {
+        checkInterrupt();
         Path path = *i;
         Path lockPath = path + ".lock";
 
@@ -87,6 +91,7 @@ PathLocks::~PathLocks()
         close(*i);
 
     for (Paths::iterator i = paths.begin(); i != paths.end(); i++) {
+        checkInterrupt();
         if (deletePaths) {
             /* This is not safe in general! */
             unlink(i->c_str());

src/libstore/references.cc

@@ -17,6 +17,7 @@ static void search(const string & s,
     for (Strings::iterator i = ids.begin();
          i != ids.end(); )
     {
+        checkInterrupt();
         if (s.find(*i) == string::npos)
             i++;
         else {
@@ -31,6 +32,8 @@ static void search(const string & s,
 void checkPath(const string & path,
     Strings & ids, Strings & seen)
 {
+    checkInterrupt();
+    
     struct stat st;
     if (lstat(path.c_str(), &st))
         throw SysError(format("getting attributes of path `%1%'") % path);

src/libstore/store.cc

@@ -133,7 +133,7 @@ void copyPath(const Path & src, const Path & dst)
             source.fd = fds[0];
             restorePath(dst, source);
             _exit(0);
-        }  catch (exception & e) {
+        } catch (exception & e) {
             cerr << "error: " << e.what() << endl;
         }
         _exit(1);        

src/libutil/archive.cc

@@ -83,6 +83,7 @@ static void dumpContents(const Path & path, unsigned int size,
     unsigned int total = 0;
     ssize_t n;
     while ((n = read(fd, buf, sizeof(buf)))) {
+        checkInterrupt();
         if (n == -1) throw SysError("reading file " + path);
         total += n;
         sink(buf, n);
@@ -200,6 +201,8 @@ static void restoreEntry(const Path & path, RestoreSource & source)
     if (s != "(") throw badArchive("expected open tag");
 
     while (1) {
+        checkInterrupt();
+
         s = readString(source);
 
         if (s == ")") {
@@ -224,6 +227,7 @@ static void restoreContents(int fd, const Path & path, RestoreSource & source)
     unsigned char buf[65536];
 
     while (left) {
+        checkInterrupt();
         unsigned int n = sizeof(buf);
         if (n > left) n = left;
         source(buf, n);
@@ -247,6 +251,8 @@ static void restore(const Path & path, RestoreSource & source)
     AutoCloseFD fd;
 
     while (1) {
+        checkInterrupt();
+
         s = readString(source);
 
         if (s == ")") {

src/libutil/util.cc

@@ -132,6 +132,7 @@ Strings readDirectory(const Path & path)
 
     struct dirent * dirent;
     while (errno = 0, dirent = readdir(dir)) { /* sic */
+        checkInterrupt();
         string name = dirent->d_name;
         if (name == "." || name == "..") continue;
         names.push_back(name);
@@ -144,6 +145,8 @@ Strings readDirectory(const Path & path)
 
 void deletePath(const Path & path)
 {
+    checkInterrupt();
+
     printMsg(lvlVomit, format("deleting path `%1%'") % path);
 
     struct stat st;
@@ -170,6 +173,8 @@ void deletePath(const Path & path)
 
 void makePathReadOnly(const Path & path)
 {
+    checkInterrupt();
+
     struct stat st;
     if (lstat(path.c_str(), &st))
 	throw SysError(format("getting attributes of path `%1%'") % path);
@@ -199,6 +204,7 @@ static Path tempName()
 Path createTempDir()
 {
     while (1) {
+        checkInterrupt();
 	Path tmpDir = tempName();
 	if (mkdir(tmpDir.c_str(), 0777) == 0) return tmpDir;
 	if (errno != EEXIST)
@@ -246,6 +252,7 @@ void Nest::open(Verbosity level, const format & f)
 
 void printMsg_(Verbosity level, const format & f)
 {
+    checkInterrupt();
     if (level > verbosity) return;
     string spaces;
     for (int i = 0; i < nestingLevel; i++)
@@ -257,6 +264,7 @@ void printMsg_(Verbosity level, const format & f)
 void readFull(int fd, unsigned char * buf, size_t count)
 {
     while (count) {
+        checkInterrupt();
         ssize_t res = read(fd, (char *) buf, count);
         if (res == -1) throw SysError("reading from file");
         if (res == 0) throw Error("unexpected end-of-file");
@@ -269,6 +277,7 @@ void readFull(int fd, unsigned char * buf, size_t count)
 void writeFull(int fd, const unsigned char * buf, size_t count)
 {
     while (count) {
+        checkInterrupt();
         ssize_t res = write(fd, (char *) buf, count);
         if (res == -1) throw SysError("writing to file");
         count -= res;
@@ -344,3 +353,11 @@ AutoCloseDir::operator DIR *()
     return dir;
 }
 
+
+volatile sig_atomic_t _isInterrupted = 0;
+
+void _interrupted()
+{
+    _isInterrupted = 0;
+    throw Error("interrupted by the user");
+}

src/libutil/util.hh

@@ -9,6 +9,7 @@
 #include <sys/types.h>
 #include <dirent.h>
 #include <unistd.h>
+#include <signal.h>
 
 #include <boost/format.hpp>
 
@@ -179,4 +180,16 @@ public:
 };
 
 
+/* User interruption. */
+
+extern volatile sig_atomic_t _isInterrupted;
+
+void _interrupted();
+
+void inline checkInterrupt()
+{
+    if (_isInterrupted) _interrupted();
+}
+
+
 #endif /* !__UTIL_H */