Effective interprocedural resource leak detection Emina Torlak and - PowerPoint PPT Presentation

Effective interprocedural resource leak detection Emina Torlak and Satish Chandra IBM T.J. Watson Research Center Hawthorne, NY

Resource leaks in Java void test(File file, String enc) throws IOException { PrintWriter out = null; Unlike memory, system resources must be try { manually managed try { out = new PrintWriter( ‣ FileOutputStream, Socket, Connection, … new OutputStreamWriter( new FileOutputStream(file), enc)); } catch (UnsupportedEncodingException ue) { out = new PrintWriter(new FileWriter(file)); } out.append(‘c’); } catch (IOException e) { } finally { if (out != null) out.close(); } } Simplified code excerpt from ANT 2

Resource leaks in Java void test(File file, String enc) throws IOException { PrintWriter out = null; Unlike memory, system resources must be try { manually managed try { out = new PrintWriter( ‣ FileOutputStream, Socket, Connection, … new OutputStreamWriter( new FileOutputStream(file), enc)); } catch (UnsupportedEncodingException ue) { out = new PrintWriter(new FileWriter(file)); } out.append(‘c’); } catch (IOException e) { close() releases } finally { the resource if (out != null) out.close(); } } Simplified code excerpt from ANT 2

Resource leaks in Java void test(File file, String enc) throws IOException { PrintWriter out = null; Unlike memory, system resources must be try { manually managed try { out = new PrintWriter( ‣ FileOutputStream, Socket, Connection, … new OutputStreamWriter( new FileOutputStream(file), enc)); } catch (UnsupportedEncodingException ue) { Manual resource management is tricky out = new PrintWriter(new FileWriter(file)); } ‣ a resource must be released on all paths out.append(‘c’); } catch (IOException e) { } finally { if (out != null) out.close(); } } Simplified code excerpt from ANT 3

Resource leaks in Java void test(File file, String enc) throws IOException { PrintWriter out = null; Unlike memory, system resources must be try { manually managed try { out = new PrintWriter( ‣ FileOutputStream, Socket, Connection, … new OutputStreamWriter( new FileOutputStream(file), enc)); } catch (UnsupportedEncodingException ue) { Manual resource management is tricky out = new PrintWriter(new FileWriter(file)); } ‣ a resource must be released on all paths out.append(‘c’); } catch (IOException e) { handle to the } finally { FileOutputStream is if (out != null) lost, so it’s never out.close(); closed } } Simplified code excerpt from ANT 3

Resource leaks in Java Unlike memory, system resources must be manually managed ‣ FileOutputStream, Socket, Connection, … Manual resource management is tricky ‣ a resource must be released on all paths Leaks lead to performance problems ‣ crashes, gradual performance degradation Excerpt from an online bug database 4

Resource leaks in Java Unlike memory, system resources must be manually managed ‣ FileOutputStream, Socket, Connection, … Manual resource management is tricky ‣ a resource must be released on all paths Leaks lead to performance problems ‣ crashes, gradual performance degradation Excerpt from an online bug database 4

T RACKER : engineering a leak detector for the real world core resource analysis algorithm heuristics for better usability ‣ inteprocedural tracking of must- ‣ ranking of leak reports access paths ‣ filtering of reports due to unlikely ‣ avoids whole-program alias exceptions analysis precision ‣ clustering of reports for nested resources scalability actionability 5

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { fis = new FileInputStream(f); Report a leak when all access isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } Tracking FileInputStream 6

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { fis = new FileInputStream(f); Report a leak when all access isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } normal flow Tracking FileInputStream 7

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } normal flow Tracking FileInputStream 7

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis, isr.sd.in }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } normal flow Tracking FileInputStream 7

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis, isr.sd.in }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased [•, { fis, isr.sd.in }] if (isr != null) resource go out of scope … isr.close(); } } normal flow Tracking FileInputStream 7

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis, isr.sd.in }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased [•, { fis, isr.sd.in }] if (isr != null) resource go out of scope … ✓ isr.close(); } } normal flow resource released: stop tracking it Tracking FileInputStream 7

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { fis = new FileInputStream(f); Report a leak when all access isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } exceptional flow Tracking FileInputStream 8

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } exceptional flow Tracking FileInputStream 8

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased if (isr != null) resource go out of scope … isr.close(); } } exceptional flow Tracking FileInputStream 8

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased [•, { fis }] if (isr != null) resource go out of scope … isr.close(); } } exceptional flow Tracking FileInputStream 8

Core resource tracking algorithm Use a local, precise aliasing void test(File f, String e) throws IOException { abstraction to track access InputStreamReader isr = null; paths to unreleased resources FileInputStream fis = null; try { • [•, { fis }] fis = new FileInputStream(f); Report a leak when all access [•, { fis }] isr = new InputStreamReader(fis, e); } finally { paths to an unreleased [•, { fis }] if (isr != null) resource go out of scope … [•, { fis }] isr.close(); } } exceptional flow Tracking FileInputStream 8