archive/{iso9660,zzip}: unlock the mutex during I/O

Similar to commit 31ab78ae8e

NEWS

@@ -3,6 +3,7 @@ ver 0.20.14 (not yet released)
   - simple: fix file corruption in the presence of mount points
 * archive
   - bz2: fix deadlock
+  - reduce lock contention, fixing lots of xrun problems
 * fix Solaris build failure
 
 ver 0.20.13 (2017/12/18)

src/archive/plugins/Iso9660ArchivePlugin.cxx

@@ -182,6 +182,8 @@ Iso9660ArchiveFile::OpenStream(const char *pathname,
 size_t
 Iso9660InputStream::Read(void *ptr, size_t read_size)
 {
+	const ScopeUnlock unlock(mutex);
+
 	int readed = 0;
 	int no_blocks, cur_block;
 	size_t left_bytes = statbuf->size - offset;

src/archive/plugins/ZzipArchivePlugin.cxx

@@ -138,6 +138,8 @@ ZzipArchiveFile::OpenStream(const char *pathname,
 size_t
 ZzipInputStream::Read(void *ptr, size_t read_size)
 {
+	const ScopeUnlock unlock(mutex);
+
 	int ret = zzip_file_read(file, ptr, read_size);
 	if (ret < 0)
 		throw std::runtime_error("zzip_file_read() has failed");
@@ -155,6 +157,8 @@ ZzipInputStream::IsEOF() noexcept
 void
 ZzipInputStream::Seek(offset_type new_offset)
 {
+	const ScopeUnlock unlock(mutex);
+
 	zzip_off_t ofs = zzip_seek(file, new_offset, SEEK_SET);
 	if (ofs < 0)
 		throw std::runtime_error("zzip_seek() has failed");