* Don't use fork() in copyPath(), but a string buffer.

src/libstore/store.cc

@@ -1,7 +1,6 @@
 #include <iostream>
 #include <algorithm>
 
-#include <sys/wait.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -126,20 +125,24 @@ void createStoreTransaction(Transaction & txn)
 
 struct CopySink : DumpSink
 {
-    int fd;
+    string s;
     virtual void operator () (const unsigned char * data, unsigned int len)
     {
-        writeFull(fd, data, len);
+        s.append((const char *) data, len);
     }
 };
 
 
 struct CopySource : RestoreSource
 {
-    int fd;
+    string & s;
+    unsigned int pos;
+    CopySource(string & _s) : s(_s), pos(0) { }
     virtual void operator () (unsigned char * data, unsigned int len)
     {
-        readFull(fd, data, len);
+        s.copy((char *) data, len, pos);
+        pos += len;
+        assert(pos <= s.size());
     }
 };
 
@@ -148,52 +151,19 @@ void copyPath(const Path & src, const Path & dst)
 {
     debug(format("copying `%1%' to `%2%'") % src % dst);
 
-    /* Unfortunately C++ doesn't support coprocedures, so we have no
+    /* Dump an archive of the path `src' into a string buffer, then
-       nice way to chain CopySink and CopySource together.  Instead we
+       restore the archive to `dst'.  This is not a very good method
-       fork off a child to run the sink.  (Fork-less platforms should
+       for very large paths, but `copyPath' is mainly used for small
-       use a thread). */
+       files. */ 
 
-    /* Create a pipe. */
-    Pipe pipe;
-    pipe.create();
-
-    /* Fork. */
-    Pid pid;
-    pid = fork();
-    switch (pid) {
-
-    case -1:
-        throw SysError("unable to fork");
-
-    case 0: /* child */
-        try {
-            pipe.writeSide.close();
-            CopySource source;
-            source.fd = pipe.readSide;
-            restorePath(dst, source);
-            _exit(0);
-        } catch (exception & e) {
-            cerr << "error: " << e.what() << endl;
-        }
-        _exit(1);        
-    }
-
-    /* Parent. */
-
-    pipe.readSide.close();
-    
     CopySink sink;
-    sink.fd = pipe.writeSide;
     {
         SwitchToOriginalUser sw;
         dumpPath(src, sink);
     }
 
-    /* Wait for the child to finish. */
+    CopySource source(sink.s);
-    int status = pid.wait(true);
+    restorePath(dst, source);
-    if (!statusOk(status))
-        throw Error(format("cannot copy `%1% to `%2%': child %3%")
-            % src % dst % statusToString(status));
 }
 
 
@@ -619,9 +589,6 @@ Path addToStore(const Path & _srcPath)
 
             if (pathExists(dstPath)) deletePath(dstPath);
 
-            /* !!! race: srcPath might change between hashPath() and
-               here! */
-            
             copyPath(srcPath, dstPath);
 
             Hash h2 = hashPath(htSHA256, dstPath);

src/libutil/archive.hh

@@ -42,6 +42,7 @@
 
 struct DumpSink 
 {
+    virtual ~DumpSink() { }
     virtual void operator () (const unsigned char * data, unsigned int len) = 0;
 };
 
@@ -50,6 +51,8 @@ void dumpPath(const Path & path, DumpSink & sink);
 
 struct RestoreSource
 {
+    virtual ~RestoreSource() { }
+    
     /* The callee should store exactly *len bytes in the buffer
        pointed to by data.  It should block if that much data is not
        yet available, or throw an error if it is not going to be