Stateless facade for FileSystemProvider SPI#895
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See [1]. Apache MINA SSHD never had that problem, but we also had no test for this. So add one just to be sure. [1] https://bugzilla.mindrot.org/show_bug.cgi?id=3950
…oader When SFTP file systems are created through the standard Java mechanism via java.nio.file.FileSystems.newFileSystem(URI, Map, Classloader), the JDK uses the ServiceLoader to find registered file system providers. It remembers any it can find via the system classloader or via the platform classloader as "installed providers" and creates only exactly one instance of them. When it cannot find a provider matching the URI scheme in the "installed providers" and a classloader is given, it then tries to find a matching file system provider using that classloader. The ServiceLoader instantiates each provider it finds to check its scheme against the URI scheme. But it doesn't remember these file system providers, so if FileSystems.newFileSystem() is called again, another instance of SftpFileSystemProvider got created. When the returned file system is used, the SftpFileSystemProvider creates an SshClient, and an I/O thread pool is set up. If multiple SftpFileSystemProviders get created, there will also be multiple SshClients, and multiple thread pools. Avoid this by registering via the FileSystemProvider SPI only a stateless facade class. All instance of this facade class delegate to a singleton SftpFileSystemProvider.
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Register a stateless facade class via the
FileSystemProviderSPI. All instance of this facade class delegateto a singleton
SftpFileSystemProvider.Fixes #743.