Synchronize access to the underlying object of Slice

This was prompted by the interactions between GL::ResourceManager and
some upcoming changes to DataFile::PackSource.  If a new Slice object is
created and tries to connect to signal_flush_required at the exact moment
another Slice is seeking and causing the signal to be emitted, the emit
and connect calls step on each others' toes and corrupt the heap.

diff --git a/source/io/base.cpp b/source/io/base.cpp
index 052d464becb6f793cb774c32e38c4fa40e686721..da2b5a98cb1c8db3f211b292137783b0c19d4e7d 100644 (file)
--- a/source/io/base.cpp
+++ b/source/io/base.cpp
@@ -8,12 +8,14 @@ namespace IO {
 
 Base::Base():
        mode(M_READ),
-       eof_flag(false)
+       eof_flag(false),
+       mutex(0)
 { }
 
 Base::~Base()
 {
        signal_deleted.emit();
+       delete mutex;
 }
 
 void Base::check_access(Mode m) const
@@ -62,5 +64,19 @@ const Handle &Base::get_handle(Mode)
        throw logic_error("Base::get_handle");
 }
 
+
+Base::Synchronize::Synchronize(Base &i):
+       io(i)
+{
+       if(!io.mutex)
+               io.mutex = new Mutex;
+       io.mutex->lock();
+}
+
+Base::Synchronize::~Synchronize()
+{
+       io.mutex->unlock();
+}
+
 } // namespace IO
 } // namespace Msp

diff --git a/source/io/base.h b/source/io/base.h
index 394a2c2306e60ebbe9f8bb7ddee0e1d4f37b4403..c58be90f7ebd039504e261105e53dc7329a1ac13 100644 (file)
--- a/source/io/base.h
+++ b/source/io/base.h
@@ -2,6 +2,7 @@
 #define MSP_IO_BASE_H_
 
 #include <sigc++/sigc++.h>
+#include <msp/core/mutex.h>
 #include "handle.h"
 #include "mode.h"
 #include "poll.h"
@@ -18,6 +19,18 @@ leaving stale pointers in an EventDispatcher.
 class Base
 {
 public:
+       /** RAII synchronization primitive.  Prevents concurrent access to the
+       target object during the lifetime of the Synchronize object. */
+       class Synchronize
+       {
+       private:
+               Base &io;
+
+       public:
+               Synchronize(Base &);
+               ~Synchronize();
+       };
+
        /** Emitted when there is no more data to be read. */
        sigc::signal<void> signal_end_of_file;
 
@@ -32,6 +45,7 @@ public:
 protected:
        Mode mode;
        bool eof_flag;
+       Mutex *mutex;
 
        Base();
 private:

diff --git a/source/io/slice.cpp b/source/io/slice.cpp
index 904f748668e472257ae383dd93330cc8fc3d4299..59a7cde301b463d492fb79ef11733702d60d512e 100644 (file)
--- a/source/io/slice.cpp
+++ b/source/io/slice.cpp
@@ -16,6 +16,7 @@ Slice::Slice(Seekable &b, SeekOffset s, SeekOffset l):
        if(s<0 || l<0)
                throw invalid_argument("Slice");
 
+       Base::Synchronize sync(below);
        mode = below.get_mode()&M_RDWR;
        below.signal_flush_required.connect(sigc::mem_fun(this, &Slice::flush));
 }
@@ -30,7 +31,12 @@ unsigned Slice::prepare_op(unsigned size, Mode m)
        check_access(m);
 
        if(sync_position)
-               seek(position, S_BEG);
+       {
+               SeekOffset pos = below.seek(start_offset+position, S_BEG)-start_offset;
+               if(pos!=position)
+                       throw runtime_error("failed to restore position");
+               sync_position = false;
+       }
 
        SeekOffset remaining = start_offset+length-position;
        if(size>remaining)
@@ -43,6 +49,7 @@ unsigned Slice::prepare_op(unsigned size, Mode m)
 
 unsigned Slice::do_write(const char *data, unsigned size)
 {
+       Base::Synchronize sync(below);
        size = prepare_op(size, M_WRITE);
        if(!size)
                return 0;
@@ -54,6 +61,7 @@ unsigned Slice::do_write(const char *data, unsigned size)
 
 unsigned Slice::do_read(char *data, unsigned size)
 {
+       Base::Synchronize sync(below);
        size = prepare_op(size, M_READ);
        if(!size)
                return 0;
@@ -67,6 +75,7 @@ unsigned Slice::do_read(char *data, unsigned size)
 
 unsigned Slice::put(char c)
 {
+       Base::Synchronize sync(below);
        if(!prepare_op(1, M_WRITE))
                return 0;
 
@@ -77,6 +86,7 @@ unsigned Slice::put(char c)
 
 int Slice::get()
 {
+       Base::Synchronize sync(below);
        if(!prepare_op(1, M_READ))
                return 0;
 
@@ -90,6 +100,7 @@ int Slice::get()
 
 SeekOffset Slice::seek(SeekOffset off, SeekType type)
 {
+       Base::Synchronize sync(below);
        off += start_offset;
        if(type==S_CUR)
                off += position;