Home > Articles > Programming

  • Print
  • + Share This
This chapter is from the book

Consider this slightly modified code:

#include "ace/Log_Msg.h"

void foo(void);

int ACE_TMAIN (int, ACE_TCHAR *[])
  ACE_TRACE (ACE_TEXT ("main"));

  ACE_LOG_MSG->priority_mask (LM_DEBUG | LM_NOTICE,
  ACE_DEBUG ((LM_INFO, ACE_TEXT ("%IHi Mom\n")));
  foo ();
  ACE_DEBUG ((LM_DEBUG, ACE_TEXT ("%IGoodnight\n")));

  return 0;

void foo(void)
  ACE_TRACE (ACE_TEXT ("foo"));

  ACE_DEBUG ((LM_NOTICE, ACE_TEXT ("%IHowdy Pardner\n")));

The following output is produced:

(1024) calling main in file `Simple2.cpp' on line 7
      Howdy Pardner

In this example, we changed the logging level at runtime so that only messages logged with LM_DEBUG and LM_NOTICE priority are displayed; all others are ignored. The LM_INFO "Hi Mom" message is not displayed, and there is no ACE_TRACE output.

We've also revealed a little more about how ACE's logging facility works. The ACE_Log_Msg class implements the log message formatting capabilities in ACE. ACE automatically maintains a thread-specific singleton instance of the ACE_Log_Msg class for each spawned thread, as well as the main thread. ACE_LOG_MSG is a shortcut for obtaining the pointer to the thread's singleton instance. All the ACE logging macros use ACE_LOG_MSG to make method calls on the correct ACE_Log_Msg instance. There is seldom a reason to instantiate an ACE_Log_Msg object directly. ACE automatically creates a new instance for each thread spawned, keeping each thread's logging output separate.

Table 3.3. ACE Logging Macros



Disabled by


Much like the assert() library call. If the test fails, an assertion message including the file name and line number, along with the test itself, will be printed and the application aborted.


((level, buffer, size [,text]))

Dumps the buffer as a string of hex digits. If provided, the optional text parameter will be printed prior to the hex string. The op_statusa is set to 0.



No message is printed, the calling function returns with value; op_status is set to value.


((level, string, ...), value)

Logs the string at the requested level. The calling function then returns with value; op_status is set to value.


ACE_ERROR((level, string, ...))

Sets the op_status to –1 and logs the string at the requested level.


ACE_DEBUG((level, string, ...))

Sets the op_status to 0 and logs the string at the requested level.


ACE_ERROR_INIT( value, flags )

Sets the op_status to value and the logger's option flags to flags. Valid flags values are defined in Table 3.5.


((level, string, ...))

Invokes ACE_ERROR() followed by a break. Use this to display an error message and exit a while or for loop, for instance.



Displays the file name, line number, and string where ACE_TRACE appears. Displays "Leaving 'string'" when the ACE_TRACE-enclosing scope exits.


We can use the ACE_Log_Msg::priority_mask() method to set the logging severity levels we desire output to be produced for: All the available logging levels are listed in Table 3.1. Each level is represented by a mask, so the levels can be combined. Let's look at the complete signature of the priority_mask() methods:

/// Get the current ACE_Log_Priority mask.
u_long priority_mask (MASK_TYPE = THREAD);

/// Set the ACE_Log_Priority mask, returns original mask.
u_long priority_mask (u_long, MASK_TYPE = THREAD);

The first version is used to read the severity mask; the second changes it and returns the original mask so it can be restored later. The second argument must be one of two values, reflecting two different scopes of severity mask setting:

  1. ACE_Log_Msg::PROCESS: Specifying PROCESS retrieves or sets the processwide mask affecting logging severity for all ACE_Log_Msg instances.

  2. ACE_Log_Msg::THREAD: Each ACE_Log_Msg instance also has its own severity mask, and this value retrieves or sets it. THREAD is technically a misnomer, as it refers to the ACE_Log_Msg instance the method is invoked on, and you can create ACE_Log_Msg instances in addition to those that ACE creates for each thread. However, that is a relatively rare thing to do, so we usually simply refer to ACE_Log_Msg instances as thread specific.

When evaluating a log message's severity, ACE_Log_Msg examines both the processwide and per instance severity masks. If either of them has the message's severity enabled, the message is logged. By default, all bits are set at the process level and none at the instance level, so all message severities are logged. To make each thread decide for itself which severity levels will be logged, set the processwide mask to 0 and allow each thread set its own per instance mask. For example, the following code disables all logging severities at the process level and enables LM_DEBUG and LM_NOTICE severities in the current thread only:

ACE_LOG_MSG->priority_mask (0, ACE_Log_Msg::PROCESS);
ACE_LOG_MSG->priority_mask (LM_DEBUG | LM_NOTICE,

A third mask maintained by ACE_Log_Msg is important when you start setting individual severity masks on ACE_Log_Msg instances. The per instance default mask is used to initialize each ACE_Log_Msg instance's severity mask. The per instance default mask is initially 0 (no severities are enabled). Because each ACE_Log_Msg instance's severity mask is set from the default value when the instance is created, you can change the default for groups of threads before spawning them. This puts the logging policy into the thread-spawning part of your application, alleviating the need for the threads to set their own level, although each thread can change its ACE_Log_Msg instance's mask at any time. Consider this example:

ACE_LOG_MSG->priority_mask (0, ACE_Log_Msg::PROCESS);
ACE_Log_Msg::enable_debug_messages ();
ACE_Thread_Manager::instance ()->spawn (service);
ACE_Log_Msg::disable_debug_messages ();
ACE_Thread_Manager::instance ()->spawn_n (3, worker);

We'll learn about thread management in Chapter 13. For now, all you need to know is that ACE_Thread_Manager::spawn() spawns one thread and that ACE_Thread_Manager::spawn_n() spawns multiple threads. In the preceding example, the processwide severity mask is set to 0 (all disabled). This means that each ACE_Log_Msg instance's mask controls its enabled severities totally. The thread executing the service() function will have the LM_DEBUG severity enabled, but the threads executing the worker() function will not.

The complete method signatures for changing the per instance default mask are:

static void disable_debug_messages
    (ACE_Log_Priority priority = LM_DEBUG);

static void enable_debug_messages
    (ACE_Log_Priority priority = LM_DEBUG);

Our example used the default argument, LM_DEBUG, in both cases. Even though the method names imply that LM_DEBUG is the only severity that can be changed, you can also supply any set of legal severity masks to either method. Unlike the priority_mask() method, which replaces the specified mask, the enable_debug_messages() and disable_debug_messages() methods add and subtract, respectively, the specified severity bits in both the calling thread's per instance mask and the per instance default severity mask.

Of course, you can use any message severity level at any time. However, take care to specify a reasonable level for each of your messages; then at runtime, you can use the priority_mask() method to enable or disable messages you're interested in. This allows you to easily overinstrument your code and then enable only the things that are useful at any particular time.

ACE_Log_Msg has a rich set of methods for recording the current state of your application. Table 3.4 summarizes the more commonly used functions. Most methods have both accessor and mutator signatures. For example, there are two op_status() methods:

int op_status(void);
void op_status(int status));

Although the method calls are most often made indirectly via the ACE logging macros, they are also available for direct use.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020